Effects of temperature and physical activity on blood flow shunts and intracardiac mixing in the toad Bufo marinus.

Blood flow in systemic (.Qsys) and pulmocutaneous (.Qpul) arteries was measured as a function of body temperature (10 degrees, 20 degrees, and 30 degrees C) at rest and following enforced physical activity in conscious, adult cane toads (Bufo marinus). Arterial and mixed venous hemoglobin concentration (CHb) and total oxygen content (Co2, tot) were measured in a separate group under identical conditions. Heart rate (fH) and total flow (.Qtot) increased significantly (P<0.001) with elevated temperature and with activity, whereas stroke volume (VS) increased (P<0.001) only with activity. .Qtot ranged about 10-fold, from 10 degrees C (rest) to 30 degrees C (activity); increases in both fH and VS contributed to the increase in .Qtot. The overall distribution of blood to the pulmocutaneous circuit (net L-R shunt) increased with both temperature and activity and was significantly correlated with .Qtot. These data indicate that blood flow distribution in toads is a direct function of cardiac output, and this is linked to relative changes in resistance in the major outflow vessels. Arterial O2 saturation (Sa) was high (mean=93%) in all conditions except activity at 30 degrees C, when it decreased to 74% and contributed to a decrease in the arteriovenous O2 difference. Venous O2 saturation (Sv) was high at rest (76%) and dropped significantly during activity to about 30% at all temperatures. Intracardiac arterial-venous mixing (systemic mixing index) showed the strongest correlation with variation in fH with minimal mixing (17%) occurring at about 50 beats min-1. The most mixing occurred at the lowest fH (13 beats min-1) and at the highest fH (103 beats min-1). The results indicate that the heart of a 0.25-kg toad becomes more efficient from an oxygen transport perspective from low fH to 50 beats min-1 and then less efficient at higher fH, contributing to an uncoupling of blood flow and metabolic rates at these high rates.     

Effect of nitric oxide synthase inhibition on regional blood flow during hyperthermia

The loss of compensatory splanchnic vasoconstriction during hyperthermia was assessed in rats after administration of either 0, 10, 30, or 100mg/kg N(w)-nitro-L-arginine methyl ester,L-NAME. Rectal temperature (T(re)), heart rate (HR), mean arterial blood pressure (MAP), breathing frequency (BF), and renal, mesenteric and caudal blood flows (Q(R), Q(M) and Q(C)) were measured until irreversible cardiovascular collapse occurred. HR, MAP and BF increased as T(re) rose to 42 degrees C, then fell as circulatory collapse occurred. As dose increased T(re) at collapse decreased. Q(M) decreased until a T(re) of 41.5-42 degrees C and then increased. Q(R) and Q(C) were unaffected by either hyperthermia orL-NAME. Inhibition of NO synthase did not prevent the circulatory collapse of heatstroke; the higher doses ofL-NAME may have exacerbated the onset of circulatory failure.     

Effects of hypoxia on the venous circulation in rainbow trout (Oncorhynchus mykiss)

Hypoxia in fish is generally associated with bradycardia while cardiac output (Q) remains unaltered or slightly increased due to a compensatory increase in stroke volume (SV). Rainbow trout (Oncorhynchus mykiss) were subjected to severe (P(W)O2=7.3+/-0.2 kPa) or mild (P(W)O2=11.5+/-0.2 kPa) hypoxia. Central venous pressure (P(ven)), dorsal aortic pressure (P(da)), heart rate (f(H)) and Q, were recorded in vivo. Both levels of hypoxia triggered a significant increase in P(ven). Severe hypoxia was associated with bradycardia and unaltered Q, whereas mild hypoxia was associated with a small but significant increase in Q and no bradycardia. These findings indicate that an increase in P(ven) promotes an increase in SV during hypoxia. Since mild hypoxia increased P(ven), Q and SV without bradycardia or reduced systemic resistance (R(sys)), we hypothesize that an active increase in venous tone serving to mobilize blood to the central venous compartment in order to increase cardiac preload and consequently SV, is an important cardiovascular trait associated with hypoxia. Pharmacological pre-treatment with prazosin (1 mg kg(-1)) did not conclusively reveal the underlying mechanisms to the observed changes in P(ven). This study discusses the influence of venous pooling, reduced R(sys) and altered venous tone on changes in P(ven) observed during hypoxia.     

Shunt dynamics in experimental atrial septal defects.

Inorder to study the hemodynamic variables involving the magnitude, direction, and timing of phasic shunt flow, both the interatrial pressure gradient and blood flow along with other pertinent hemodynamic variables were measured instantaneously across a surgically created atrial septal defect (ASD) in seven awake dogs. Atrial and ventricular pacing and infusion of phenylephrine and isoproterenol were used to alter hemodynamic conditions. The wave form of phasic ASD flow was similar both in configuration and timing to the interatrial pressure gradient. During the cardiac cycle, both left-to-right (L-R) and right-to-left (R-L) shunting occurred: atrial contraction augmented L-R flow; the onset of ventricular contraction was associated with R-L flow; during the latter part of ventricular contraction, flow returned to L-R with the maximum L-R shunting occurring in early diastole. Tachycardia, infusion of phenylephrine and isoproterenol did not alter the phasic flow pattern. Both spontaneous and positive pressure respiration decreased net L-R shunting.     

Finger dexterity, skin temperature, and blood flow during auxiliary heating in the cold.

The primary purpose of the present study was to compare the effectiveness of two forms of hand heating and to discuss specific trends that relate finger dexterity performance to variables such as finger skin temperature (T(fing)), finger blood flow (Q(fing)), forearm skin temperature (T(fsk)), forearm muscle temperature (Tfmus), mean weighted body skin temperature (Tsk), and change in body heat content (DeltaH(b)). These variables along with rate of body heat storage, toe skin temperature, and change in rectal temperature were measured during direct and indirect hand heating. Direct hand heating involved the use of electrically heated gloves to keep the fingers warm (heated gloves condition), whereas indirect hand heating involved warming the fingers indirectly by actively heating the torso with an electrically heated vest (heated vest condition). Seven men (age 35.6 +/- 5.6 yr) were subjected to each method of hand heating while they sat in a chair for 3 h during exposure to -25 degrees C air. Q(fing) was significantly (P < 0.05) higher during the heated vest condition compared with the heated gloves condition (234 +/- 28 and 33 +/- 4 perfusion units, respectively), despite a similar T(fing) (which ranged between 28 and 35 degrees C during the 3-h exposure). Despite the difference in Q(fing), there was no significant difference in finger dexterity performance. Therefore, finger dexterity can be maintained with direct hand heating despite a low Q(fing). DeltaH(b), Tsk, and T(fmus) reached a low of -472 +/- 18 kJ, 28.5 +/- 0.3 degrees C, and 29.8 +/- 0.5 degrees C, respectively, during the heated gloves condition, but the values were not low enough to affect finger dexterity.     

Effects of lethal levels of environmental hypercapnia on cardiovascular and blood-gas status in yellowtail,Seriola quinqueradiata

The cardiorespiratory responses were examined in yellowtail, Seriola quinqueradiata exposed to two levels of hypercapnia (seawater equilibrated with a gas mixture containing 1% CO(2) (water PCO(2) = 7 mmHg) or 5% CO(2) (38 mmHg)) for 72 hr at 20 degrees C. Mortality was 100% within 8 hr at 5% CO(2), while no fish died at 1% CO(2). No cardiovascular variables (cardiac output, Q; heart rate, HR; stroke volume, SV and arterial blood pressure, BP) significantly changed from pre-exposure values during exposure to 1% CO(2). Arterial CO(2) partial pressure (PaCO(2)) significantly increased (P < 0.05), reaching a new steady-state level after 3 hr. Arterial blood pH (pHa) decreased initially (P < 0.05), but was subsequently restored by elevation of plasma bicarbonate ([HCO(3)(-)]). Arterial O(2) partial pressure (PaO(2)), oxygen content (CaO(2)), and hematocrit (Hct) were maintained throughout the exposure period. In contrast, exposure to 5% CO(2) dramatically reduced Q (P < 0.05) through decreasing SV (P < 0.05), although HR did not change. BP was transiently elevated (P < 0.05), followed by a precipitous fall before death. The pHa was restored incompletely despite a significant increase in [HCO(3)(-)]. PaO(2) decreased only shortly before death, whereas CaO(2) kept elevated due to a large increase in Hct (P < 0.05). We tentatively conclude that cardiac failure is a primary physiological disorder that would lead to death of fish subjected to high environmental CO(2) pressures.     

Evidence that neurotensin mediates postprandial intestinal hyperemia in the python, Python regius

Digestion of large meals in pythons produces substantial increases in heart rate and cardiac output, as well as a dilation of the mesenteric vascular bed leading to intestinal hyperemia, but the mediators of these effects are unknown. Bolus intra-arterial injections of python neurotensin ([His(3), Val(4), Ala(7)]NT) (1 - 1,000 pmol/kg) into the anesthetized ball python Python regius (n = 7) produced a dose-dependent vasodilation that was associated with a decrease in systemic pressure (P(sys)) and increase in systemic blood flow (Q(sys)). There was no effect on pulmonary pressure and conductance. A significant (P < 0.05) increase in heart rate (f(H)) and total cardiac output (Q(tot)) was seen only at high doses (>30 pmol/kg). The systemic vasodilation and increase in Q(tot) persisted after beta-adrenergic blockade with propranolol, but the rise in f(H) was abolished. Also, the systemic vasodilation persisted after histamine H(2)-receptor blockade. In unanesthetized pythons (n = 4), bolus injection of python NT in a dose as low as 1 pmol/kg produced a significant increase in blood flow to the mesenteric artery (177% +/- 54%; mean +/- SE) and mesenteric conductance (219% +/- 74%) without any increase in Q(sys), systemic conductance, P(sys), and f(H). The data provide evidence that NT is an important hormonal mediator of postprandial intestinal hyperemia in the python, but its involvement in mediating the cardiac responses to digestion may be relatively minor.     

Stroke volume during exercise: interaction of environment and hydration

Euhydrated and dehydrated subjects exercised in a hot and a cold environment with our aim to identify factors that relate to reductions in stroke volume (SV). We hypothesized that reductions in SV with heat stress are related to the interaction of several factors rather than the effect of elevated skin blood flow. Eight male endurance-trained cyclists [maximal O(2) consumption (VO(2 max)) 4.5 +/- 0.1 l/min; means +/- SE] cycled for 30 min (72% VO(2 max)) in the heat (H; 35 degrees C) or the cold (C; 8 degrees C) when euhydrated or dehydrated by 1.5, 3.0, or 4.2% of their body weight. When euhydrated, SV and esophageal temperature (T(es) 38. 2-38.3 degrees C) were similar in H and C, whereas skin blood flow was much higher in H vs. C (365 +/- 64% higher; P < 0.05). With each 1% body weight loss, SV declined 6.4 +/- 1.3 ml (4.8%) in H and 3.4 +/- 0.4 ml (2.5%) in C, whereas T(es) increased 0.21 +/- 0.02 and 0. 10 +/- 0.02 degrees C in H and C, respectively (P < 0.05). However, reductions in SV were not associated with increases in skin blood flow. The reduced SV was highly associated with increased heart rate and reduced blood volume in both H (R = 0.96; P < 0.01) and C (R = 0. 85; P < 0.01). In conclusion, these results suggest that SV is maintained in trained subjects during exercise in euhydrated conditions despite large differences in skin blood flow. Furthermore, the lowering of SV with dehydration appears largely related to increases in heart rate and reductions in blood volume.     

Effects of airflow and work load on cardiovascular drift and skin blood flow

Cardiovascular drift (CVD) can be defined as a progressive increase in heart rate (HR), decreases in stroke volume (SV) and mean arterial pressure (MAP), and a maintained cardiac output (Q) during prolonged exercise. To test the hypothesis that the magnitude of CVD would be related to changes in skin blood flow ( SkBF ), eight healthy, moderately trained males performed 70-min bouts of cycle ergometry in a 2 X 2 assortment of airflows (less than 0.2 and 4.3 m X s-1) and relative work loads (43.4% and 62.2% maximal O2 uptake). Ambient temperature and relative humidity were controlled to mean values of 24.2 +/- 0.8 degrees C and 39.5 +/- 2.4%, respectively. Q, HR, MAP, SkBF , skin and rectal temperatures, and pulmonary gas exchange were measured at 10-min intervals during exercise. Between the 10th and 70th min during exercise at the higher work load with negligible airflow, HR and SkBF increased by 21.6 beats X min-1 and 14.0 ml X 100 ml-1 X min-1, respectively, while SV and MAP decreased by 16.4 ml and 11.3 mmHg. The same work load in the presence of 4.3 m X s-1 airflow resulted in nonsignificant changes of 7.6 beats X min-1, 4.0 ml X (100 ml-1 X min)-1, -2.7 ml, and -1.7 mmHg for HR, SkBF , SV, and MAP. Since nonsignificant changes in HR, SkBF , SV, and MAP were observed at the lower work load in both airflow conditions, the results emphasize that CVD occurs only in conditions which combine high metabolic and thermal circulatory demands.(ABSTRACT TRUNCATED AT 250 WORDS)     

15 degrees head-down tilt attenuates the postexercise reduction in cutaneous vascular conductance and sweating and decreases esophageal temperature recovery time.

The following study examined the effect of 15 degrees head-down tilt (HDT) on postexercise heat loss and hemodynamic responses. We tested the hypothesis that recovery from dynamic exercise in the HDT position would attenuate the reduction in the heat loss responses of cutaneous vascular conductance (CVC) and sweating relative to upright seated (URS) recovery in association with an augmented hemodynamic response and an increased rate of core temperature decay. Seven male subjects performed the following three experimental protocols: 1) 60 min in the URS posture followed by 60 min in the 15 degrees HDT position; 2) 15 min of cycle ergometry at 75% of their predetermined V(O2 peak) followed by 60 min of recovery in the URS posture; or 3) 15 min of cycle ergometry at 75% of their predetermined V(O2 peak) followed by 60 min of recovery in the 15 degrees HDT position. Mean skin temperature, esophageal temperature (T(es)), skin blood flow, sweat rate, cardiac output (CO), stroke volume (SV), heart rate (HR), total peripheral resistance, and mean arterial pressure (MAP) were recorded at baseline, end exercise, 2, 5, 8, 12, 15, and 20 min, and every 5 min until end of recovery (60 min). Without preceding exercise, HDT decreased HR and increased SV (P < or = 0.05). During recovery after exercise, a significantly greater MAP, SV, CVC, and sweat rate and a significantly lower HR were found with HDT compared with URS posture (P < or = 0.05). Subsequently, a significantly lower T(es) was observed with HDT after 15 min of recovery onward (P < or = 0.05). At the end of 60 min of recovery, T(es) remained significantly elevated above baseline with URS (P < or = 0.05); however, T(es) returned to baseline with HDT. In conclusion, extended recovery from dynamic exercise in the 15 degrees HDT position attenuates the reduction in CVC and sweating, thereby significantly increasing the rate of T(es) decay compared with recovery in the URS posture.     

Computational model of the fluid dynamics in systemic-to-pulmonary shunts

A systemic-to-pulmonary shunt is a connection created between the systemic and pulmonary arterial circulations in order to improve pulmonary perfusion in children with congenital heart diseases. Knowledge of the relationship between pressure and flow in this new, surgically created, cardiovascular district may be helpful in the clinical management of these patients, whose survival is critically dependent on the blood flow distribution between the pulmonary and systemic circulations. In this study a group of three-dimensional computational models of the shunt have been investigated under steady-state and pulsatile conditions by means of a finite element analysis. The model is used to quantify the effects of shunt diameter (D), curvature, angle, and pulsatility on the pressure-flow (DeltaP-Q) relationship of the shunt. Size of the shunt is the main regulator of pressure-flow relationship. Innominate arterial diameter and angles of insertion have less influence. Curvature of the shunt results in lower pressure drops. Inertial effects can be neglected. The following simplified formulae are derived: DeltaP=(0. 097Q+0.521Q(2))/D(4) and DeltaP=(0.096Q+0.393Q(2))/D(4) for the different shunt geometries investigated (straight and curved shunts, respectively).     

Cardiac function and critical swimming speed of the winter flounder (Pleuronectes americanus) at two temperatures

Using Transonic flow probes and a uniquely designed swimming flume, we directly measured cardiac parameters (Q, cardiac output; SV, stroke volume; and fH, heart rate) in winter flounder (Pleuronectes americanus) before and during critical swim speed (Ucrit) tests at 4 and 10 degrees C. Resting Q, SV and fH averaged 9.8 ml min(-1) kg(-1), 0.5 ml kg(-1) (1.0 ml g ventricle(-1)) and 21 beats min(-1) at 4 degrees C and 15.5 ml min(-1) kg(-1), 0.5 ml kg(-1) (0.95 ml g ventricle(-1)) and 34 beats min(-1) at 10 degrees C (Q10 values of 2.13, 0.91 and 2.35, for Q, SV and fH, respectively). Cardiac output, SV and fH increased by approx. 170%, 70% and 60% at both temperatures during the Ucrit test. However, cardiac parameters generally reached near maximal levels almost immediately upon swimming and remained at these levels until Ucrit (0.65 +/- 0.06 bl s(-1) at 4 degrees C and 0.73 +/ -0.07 bl s(-1) at 10 degrees C). This rapid rise in cardiac function to near maximal levels did not appear to be the result of stress alone, as Q only fell slightly when flounder were swum for 75 min at < 0.4 bl s(-1), speeds at which they appeared to swim comfortably. Our results suggest that both Q and Ucrit have been significantly overestimated in flatfishes, and that "lift-off"/slow swimming is energetically expensive. Furthermore, they show that maximum and resting stroke volume (per g of ventricle) are extremely high in the flounder as compared with other teleosts.     

Myocardial function defined by strain rate and strain during alterations in inotropic states and heart rate

For porcine myocardium, ultrasonic regional deformation parameters, systolic strain (epsilon(sys)) and peak systolic strain rate (SR(sys)), were compared with stroke volume (SV) and contractility [contractility index (CI)] measured as the ratio of end-systolic strain to end-systolic wall stress. Heart rate (HR) and contractility were varied by atrial pacing (AP = 120-180 beats/min, n = 7), incremental dobutamine infusion (DI = 2.5-20 microg. kg(-1). min(-1), n = 7), or continuous esmolol infusion (0.5 mg. kg(-1). min(-1)) + subsequent pacing (120-180 beats/min) (EI group, n = 6). Baseline SR(sys) and epsilon(sys) averaged 5.0 +/- 0.4 s(-1) and 60 +/- 4%. SR(sys) and CI increased linearly with DI (20 microg. kg(-1). min(-1); SR(sys) = 9.9 +/- 0.7 s(-1), P < 0.0001) and decreased with EI (SR(sys) = 3.4 +/- 0.1 s(-1), P < 0.01). During pacing, SR(sys) and CI remained unchanged in the AP and EI groups. During DI, epsilon(sys) and SV initially increased (5 microg. kg(-1). min(-1); epsilon(sys) = 77 +/- 6%, P < 0.01) and then progressively returned to baseline. During EI, SV and epsilon(sys) decreased (epsilon(sys) = 38 +/- 2%, P < 0.001). Pacing also decreased SV and epsilon(sys) in the AP (180 beats/min; epsilon(sys) = 36 +/- 2%, P < 0.001) and EI groups (180 beats/min; epsilon(sys) = 25 +/- 3%, P < 0.001). Thus, for normal myocardium, SR(sys) reflects regional contractile function (being relatively independent of HR), whereas epsilon(sys) reflects changes in SV.     

Concurrent reductions in blood pressure and metabolic rate during fasting in the unrestrained SHR

Arctic ground squirrels (Spermophilus parryii) overwinter in hibernaculum conditions that are substantially below freezing. During torpor, captive arctic ground squirrels displayed ambient temperature (T(a))-dependent patterns of core body temperature (T(b)), metabolic rate (TMR), and metabolic fuel use, as determined by respiratory quotient (RQ). At T(a) 0 to -16 degrees C, T(b) remained relatively constant, and TMR rose proportionally with the expanding gradient between T(b) and T(a), increasing >15-fold from a minimum of 0.0115 +/- 0.0012 ml O(2). g(-1). h(-1). At T(a) 0-20 degrees C, T(b) increased with T(a); however, TMR did not change significantly from T(b) 0 to 12 degrees C, indicating temperature-independent inhibition of metabolic rate. The overall change in TMR from T(b) 4 to 20 degrees equates to a Q(10) of 2.4, but within this range of T(b), Q(10) changed from 1.0 to 14.1. During steady-state torpor at T(a) 4 and 8 degrees C, RQ averaged 0.70 +/- 0.013, indicating exclusive lipid catabolism. At T(a) -16 and 20 degrees C, RQ increased significantly to >0.85, consistent with recruitment of nonlipid fuels. RQ was negatively correlated with maximum torpor bout length. For T(a) values <0 degrees C, this relationship supports the hypothesis that availability of nonlipid metabolic fuels limits torpor duration in hibernating mammals; for T(a) values >0 degrees C, hypotheses linked to body temperature are supported. Because anterior body temperatures differ from core, overall, the duration torpor can be extended in hibernating mammals may be dependent on brain temperature.     

Metabolic and cardiovascular adjustment to work in air and water at 18, 25, and 33 degrees C.

By use of successive increments of discontinuous work with an arm-leg cycle ergometer the VO2, Q, SV, and HR were studied in six male subjects at rest and during exercise in air and in water at 18, 25, and 33 degrees C. The Q values obtained by CO2 rebreathing were reproducible. VO2 was linearly related to work with the plots for air and 33 degrees C water being similar. However, during work in 25 and 18 degrees C water, the VO2 averaged 9.0% (150 ml) and 25.3% (400 ml) higher, respectively, than values observed in 33 degrees C water, with the largest differences observed in leaner subjects. The plot of HR-VO2 was linear and almost identical during work in air and 33 degrees C water, but shifted significantly to the right in cooler water. VO2 averaged 250-700 ml higher in cold water compared to air and 33 degrees C water at a given mean heart rate. The Q vs. VO2 line was similar during work in air and in water with no effect of water or temperature. At similar levels of VO2, SV was significantly larger (P less than 0.05) in 25 and 18 degrees C water than in air or 33 degrees C water. Consequently, the reduction in heart rate during work in cold water was entirely compensated for by a proportionate increase in the SV of the heart. Q was therefore maintained at similar levels of energy expenditure in air and in 18, 25, and 30 degrees C water.     

Unappreciated tolerance to high ambient temperatures in a widely distributed desert rodent, Dipodomys merriami

A long-held assertion has been that nocturnality is an escape mechanism for many nocturnal desert rodents because of limited tolerances to heat. To test this claim, we used a treadmill to examine the tolerances to high ambient temperatures (T(a)'s) of one subspecies of desert rodent, Merriam's kangaroo rat, Dipodomys merriami merriami, from contrasting environments. We simultaneously measured body temperature (T(b)), evaporative water loss, and metabolic rates at an ecologically relevant speed (0.6 km h(-1)) at different ambient temperatures (Ta=25 degrees -42.5 degrees C). We hypothesized that kangaroo rats from a more xeric site would have greater abilities to remain active and maintain stable T(b) than those from a more mesic site, but mesic- and xeric-site animals had comparable tolerances and were active until Tb=42 degrees C. At Ta=42.5 degrees C, however, T(b) of mesic-site animals increased more quickly than in xeric-site animals. Although most animals could not run more than 18 min at Ta=42.5 degrees C, most could run at Ta=40 degrees C for at least 30 min. Benefits of nocturnality for this species may reside more in purposes of water conservation and avoidance of predation and less on the direct regulation of T(b), as T(b) is more labile than commonly thought.     

Hypohydration effect on finger skin temperature and blood flow during cold-water finger immersion.

This study was conducted to determine whether hypohydration (Hy) alters blood flow, skin temperature, or cold-induced vasodilation (CIVD) during peripheral cooling. Fourteen subjects sat in a thermoneutral environment (27 degrees C) during 15-min warm-water (42 degrees C) and 30-min cold-water (4 degrees C) finger immersion (FI) while euhydrated (Eu) and, again, during Hy. Hy (-4% body weight) was induced before FI by exercise-heat exposure (38 degrees C, 30% relative humidity) with no fluid replacement, whereas during Eu, fluid intake maintained body weight. Finger pad blood flow [as measured by laser-Doppler flux (LDF)] and nail bed (T(nb)), pad (T(pad)), and core (T(c)) temperatures were measured. LDF decreased similarly during Eu and Hy (32 +/- 10 and 33 +/- 13% of peak during warm-water immersion). Mean T(nb) and T(pad) were similar between Eu (7.1 +/- 1.0 and 11.5 +/- 1.6 degrees C) and Hy (7.4 +/- 1.3 and 12.6 +/- 2.1 degrees C). CIVD parameters (e.g., nadir, onset time, apex) were similar between trials, except T(pad) nadir was higher during Hy (10.4 +/- 3.8 degrees C) than during Eu (7.9 +/- 1.6 degrees C), which was attributed to higher T(c) in six subjects during Hy (37.5 +/- 0.2 degrees C), compared with during Eu (37.1 +/- 0.1 degrees C). The results of this study provide no evidence that Hy alters finger blood flow, skin temperature, or CIVD during peripheral cooling.     

Gender affects sympathetic and hemodynamic response to postural stress

We tested the hypothesis that differences in sympathetic reflex responses to head-up tilt (HUT) between males (n = 9) and females (n = 8) were associated with decrements in postural vasomotor responses in women. Muscle sympathetic nerve activity (MSNA; microneurography), heart rate, stroke volume (SV; Doppler), and blood pressure (Finapres) were measured during a progressive HUT protocol (5 min at each of supine, 20 degrees, 40 degrees, and 60 degrees ). MSNA and hemodynamic responses were also measured during the cold pressor test (CPT) to examine nonbaroreflex neurovascular control. SV was normalized to body surface area (SV(i)) to calculate the index of cardiac output (Q(i)), and total peripheral resistance (TPR). During HUT, heart rate increased more in females versus males (P < 0.001) and SV(i) and Q(i) decreased similarly in both groups. Mean arterial pressure (MAP) increased to a lesser extent in females versus males in the HUT (P < 0.01) but increases in TPR during HUT were similar. MSNA burst frequency was lower in females versus males in supine (P < 0.03) but increased similarly during HUT. Average amplitude/burst increased in 60 degrees HUT for males but not females. Both males and females demonstrated an increase in MAP as well as MSNA burst frequency, mean burst amplitude, and total MSNA during the CPT. However, compared with females, males demonstrated a greater neural response (DeltaTotal MSNA) due to a larger increase in mean burst amplitude (P < 0.05). Therefore, these data point to gender-specific autonomic responses to cardiovascular stress. The different MSNA response to postural stress between genders may contribute importantly to decrements in blood pressure control during HUT in females.     

Single-breath DLCO maneuver causes cardiac output to fall during and after cycling

The purpose of this study was to evaluate the influence of the single-breath pulmonary diffusing capacity (DLCO) breath-hold maneuver on central hemodynamics. Ten men (mean age 24 yr) were studied at rest, during 40 min of cycling at 40 and 60% of peak O2 uptake, and 10 min into recovery. DLCO was measured in the seated position during a 10-s breath hold at total lung capacity. At rest the breath hold caused a significant fall in stroke volume (SV, -16%) and an increase in heart rate (HR, +20%) with no change in cardiac output (Q). The resting DLCO of 36.5 ml.min-1.mmHg-1 increased by 28 and 48%, respectively, during the low- and moderate-intensity cycling. The breath hold while cycling caused a significant decrease in SV and Q, but HR did not change. Likewise, during recovery SV and Q fell with the breath hold but again HR did not change. A significant fall in systolic (-17%), diastolic (-12.5%), and mean arterial pressure (-15%) occurred during the breath hold at rest and during and after the exercise. The reduction observed in SV and blood pressure most likely reflected a decrease in venous return. The differences observed in the HR response before, compared with during and after exercise, were consistent with a resetting or shift in the operating point of the arterial baroreflex. Because blood flow fell during the exercise and recovery breath-hold maneuver, the "true" DLCO may have been underestimated during and after cycling.     

Evaluation of the use of an integration-type laser-Doppler flowmeter with a temperature-loading instrument for measuring skin blood flow in elderly subjects during cooling load: comparison with younger subjects

An integration-type laser-Doppler flowmeter, equipped with a temperature-load instrument, for measuring skin blood flow (ILD-T), and analytical parameters developed in a previous study were used to compare changes in the skin blood flow in the forehead and cheek in elderly subjects (in their 60s and 70s) with those in younger subjects (in their teens to 50s). Age-related differences in skin blood flow in the forehead and cheek in response to cooling were evaluated in 90 healthy women in their teens to 70s (mean age: 17.2 +/- 0.33 years for teenagers; 24.3 +/- 0.76 years for those aged 20-29 years; 34.8 +/- 1.12 years for those aged 30-39 years; 43.3 +/- 0.78 years for those aged 40-49 years; 53.8 +/- 1.13 years for those aged 50-59 years; 63.5 +/- 0.55 years for those aged 60-69 years; 72.2 +/- 0.70 years for those aged 70-79 years). The measurement was performed continuously for 5 min: for 1 min at a sensor temperature of 30 degrees C, for 2 min after the setting of the sensor temperature had been changed to 10 degrees C, and for 2 min after the temperature setting had been cancelled. The parameters analyzed were (1) skin temperature in a resting state before measurement ( T(rest)), (2) mean skin blood flow in 1 min at a sensor temperature of 30 degrees C ( F(30 degrees C)), (3) minimum skin blood flow at a sensor temperature of 10 degrees C ( F(min)), (4) slope of the blood flow plot during the period from the beginning of cooling at 10 degrees C to F(min) ( S(fall)), (5) time required for the sensor temperature to reach 10 degrees C (Delta t(s)), (6) maximum skin blood flow during the period from the end of cooling to the end of measurement ( F(max)), (7) slope of the blood flow plot during the period from F(min) to F(max) ( S(rise)), (8) rate of decrease of the skin blood flow during cooling: FDR = ( F(min)/ F(30 degrees C))x100, (9) recovery rate of the skin blood flow after the end of cooling: FRR = ( F(max)/ F(30 degrees C))x100. When correlations among the above nine parameters were evaluated by combining all age groups, significant correlations ( P < 0.01) were observed between F(30 degrees C) and F(min), F(30 degrees C) and F(max), F(30 degrees C) and S(fall), F(min) and F(max), and F(max) and S(rise) in the forehead. In the cheek, significant correlations ( P < 0.01) were observed in all these combinations except between F(max) and S(rise). When these analytical parameters were compared among the age groups, F(30 degrees C), T(rest), F(max), and S(rise) decreased significantly ( P < 0.02 for F(30 degrees C) and T(rest), P < 0.01 for F(max) and S(rise)) and S(fall) increased significantly ( P < 0.03) in the forehead with aging. However, no significant change with aging was observed in FDR, Delta t(s), F(min), and FRR. In the cheek, FDR increased significantly ( P < 0.03), and S(rise) decreased significantly ( P < 0.01) with aging. However, no significant change with aging was observed in F(30 degrees C), T(rest), F(max), S(fall), Delta t(s), F(min), and FRR. Thus, the decrease in the skin blood flow during cooling showed no marked quantitative change with age, but, with aging, the rate of this decrease was clearly reduced in the forehead. In the cheek, on the other hand, the skin blood flow decreased markedly with aging, but no clear change was observed in the rate of this decrease. By using ILD-T and examining various parameters obtained, the skin hemodynamics in the forehead and cheek during cooling from 30 degrees C to 10 degrees C could be analyzed, and differences in the hemodynamics between the forehead and cheek and between elderly and younger individuals were clarified. This instrument is expected to be clinically useful.