Surgery increases fetal plasma prostacyclin

Pulmonary arterial prostacyclin (as 6-keto-PGF_1α) concentrations of near term, fetakl lambs and goats were determined following fetal surgery and 24, 48, and 72 hrs later. Blood gases, pH, and arterial pressure were determined also. At the end of 2.5 hrs of surgery including exteriorization of the uterus and fetal thorocotomy, pulmonary arterial concentrations of 6-keto-PGF_1α was 948 ± 92 (SEM) pg/ml of blood. Twenty-four hrs later it had fallen to 435 ± 92 pg/ml and remained constant for the duration of monitoring. Maternal arterial 6-keto-PGF_1α concentration was much lower (105 ± 20 pg/ml of blood). No significance changes in fetal Pa_O2, Pa_CO2, pH, or arterial pressure were observed, although Pa_CO2 appeared to be elevated and pH reduced following surgery. These values normalized within 24 hrs. We conclude that surgical perturbation increases fetal arterial prostacyclin concentration. Increased prostacyclin levels are transient, reaching stable values within 24 hrs following completion of extensive surgery.     

Prostacyclin (PGI2) mediates hypoxic relaxation of bovine coronary arterial strips

Bovine coronary arterial strips (BCA) exhibiting spontaneous tone, relax in response to a decrease in the PO₂ of the batching medium. Experiments were performed to determine if prostaglandins (PGs) mediate the oxygen-induced changes in tension. BCA were equilibrated in Krebs-bicarbonate solution at 37 °C gassed with 95% O₂, 5% CO₂ and tension was measured isometrically. When the PO₂ of the bathing medium was decreased, BCA exhibited reversible reductions in tension. Switching from 95% O₂, 5% CO₂ to 95% N₂, 5% CO₂ (anoxia) elicited an initial relaxation followed by a contraction. In contrast, a change to 5% O₂, 5% CO₂, 90% N₂ (hypoxia) was followed by a sustained relaxation. Re-introduction of O₂ to anoxic strips produced a biphasic response: relaxation followed by contraction. Indomethacin or eicosatetraynoic acid (EYA) increased tone and inhibited the relaxation produced by anoxia or hypoxia. Indomethacin or EYA did not inhibit the relaxation of anoxic strips during re-introduction of O₂, but did inhibit the contraction partially. Relaxation of arterial strips to arachidonic acid (AA) was similar to relaxation to prostacyclin (PGI₂). Anoxia limited the relaxation to AA but not to PGI₂. We conclude that PG synthesis contributes to the basal tone and the hypoxia-induced relaxation of CBA. In addition, hypoxia, unless severe, does not prevent the conversion of AA to PGI₁.     

Effect of prostaglandins E2 and F2α on umbilical blood flow and fetal hemodynamics

The hemodynamic effects of PGF_2α, PGE₂, and norepinephrine injected into the umbilical arterial circulation were compared in nine fetal lambs in utero. Umbilical blood flow was measured with radioactive microspheres and an electromagnetic flow transducer implanted on the distal aorta of the fetus after ligation of external iliac arteries and other accessible distal aortic branches.PGF_2α and norepinephrine increased fetal arterial pressure and umbilical blood flow while umbilical vascular resistance increased slightly (PGF_2α) or not at all (norepinephrine). PGE₂ increased fetal arterial pressure, decreased umbilical blood flow, and exerted a profound active vasoconstrictor effect on the fetal placental bed. Our data taken together with the observations of others suggest that prostaglandins may play a role in the circulatory adaptations of the fetus at birth and that PGE₂ in high concentrations is likely to have deleterious hemodynamic consequences in the fetus in utero.     

Effect of maternal undernutrition in early gestation on ovine fetal blood pressure and cardiovascular reflexes

Human epidemiological and animal experimental studies suggest that maternal undernutrition during pregnancy may alter cardiovascular development of the offspring. The extent to which these effects involve changes in fetal cardiovascular function and whether they are necessarily linked to reduced fetal growth is unknown. In sheep, we investigated the effect of a 15% reduction in maternal global nutrition for the first 70 days of gestation (term = 147 days) on fetal blood pressure development, baroreflex control of fetal heart rate (FHR), and cardiovascular responses to acute hypoxemia in late gestation. Basal mean arterial pressure (P < 0.05), systolic blood pressure (P < 0.05), diastolic blood pressure (P < 0.05), and rate-pressure product (P < 0.001) were significantly lower in fetuses of nutritionally restricted ewes (R) compared with controls (C). FHR was not altered. The operating point for the fetal baroreflex was significantly lower in R fetuses compared with C (P < 0.01), but there was no difference between the groups in the cardiovascular response to hypoxemia. We conclude that mild maternal undernutrition alters fetal cardiovascular development, producing low blood pressure and resetting of baroreflex control mechanisms. This effect occurs without any changes in fetal growth or blood gas status.     

Haemoglobin function and respiratory status of the Port Jackson shark,<Emphasis Type="Italic"> Heterodontus portusjacksoni</Emphasis>, in response to lowered salinity

Haemoglobin function and respiratory status of sub-adult sharks, Heterodontus portusjacksoni was investigated for up to 1 week following transfer from 100% to either 75% or 50% seawater. Metabolic rates were unusually low and arterial–venous differences in blood O₂ small. Haemodilution from osmotic inflow lowered haematocrit and reduced blood O₂ content by up to 50%. There was no change in O₂ consumption rate, blood O₂ partial pressure, cardiac output, or the arterial-venous O₂ content difference, and thus O₂ delivery was maintained. Ventilation was acutely elevated but returned to normal within 24 h. The O₂ delivery to the tissues was facilitated by decreased blood O₂-affinity that could not be simply ascribed to changes in the osmolyte concentration. The Hb was unaffected by changes in intra-erythrocyte fluid urea or trimethylamine-N-oxide (TMAO) but was sensitive to changes in NaCl. The Bohr shifts in whole blood were low and there was little role for pH in modulating O₂ transport. Venous Hb saturation remained close to 65%, at the steepest part of the in vivo O₂ equilibrium curve, such that O₂ unloading could be facilitated by small reductions in pressure without increasing cardiac or ventilatory work. H. portusjacksoni tolerated 50% seawater for at least 1 month, but there was little evidence of respiratory responses being adaptive which instead appeared to be consequential on changes in osmotic and ionic status.Abbreviations a–v arterial–venous - CO ₂ CO₂ content - C _a O ₂ content of O₂ in arterial blood - C _v O ₂ content of O₂ in venous blood - %E branchial O₂ extraction efficiency - f _v ventilatory frequency - GTP guanosine triphosphate - Hct haematocrit - [Hb] haemoglobin concentration - ITP inosine triphosphate - met[Hb] methaemoglobin - oxygen consumption - NTP nucleoside triphosphate - OEC oxygen equilibrium curve - P _a O ₂ partial pressure of O₂ in arterial blood - P _e O ₂ partial pressure of expired O₂ - P _i O ₂ partial pressure of inspired O₂ - P _in O ₂ inflow partial pressure of O₂ - PO ₂ partial pressure of O₂ - P _out O ₂ outflow partial pressure of O₂ - pH _a arterial blood pH - pH _pl whole blood pH - PV plasma volume - P _v CO ₂ partial pressure of CO₂in venous blood - P _v O ₂ partial pressure of O₂in venous blood - cardiac output - SW seawater - TMAO trimethylamine-N-oxide - ventilation volume Communicated by G. Heldmaier     

Mechanisms of stimulation of pulmonary prostacyclin synthesis at birth

In order to investigate the mechanism behind ventilation-induced pulmonary prostacyclin production at birth, chloralose anesthetized, exteriorized, fetal lambs were ventilated with a gas mixture that did not change blood gases (fetal gas) and unventilated fetal lungs were perfused with blood containing increased O₂ and decreased CO₂. Ventilation with fetal gas (3%O₂, 5%CO₂) increased net pulmonary prostacyclin (as 6-keto-PGF_1α production from −5.1 ± 4.4 to +12.6 ± 7.6 ng/kg·min. When ventilation was stopped, net pulmonary prostacyclin production returned to nondetectable levels. Ventilation with gas mixtures which increased pulmonary venous P_O2 and decreased P_O2 also stimulated pulmonary prostacyclin production, but did not have greater effects than did ventilation with fetal gas. In order to determine if increasing P_O2 or decreasing P_CO2 could stimulate pulmonary prostacyclin production independently from ventilation, unventilated fetal lamb lungs were perfused with blood that had P_O2 and P_CO2 similar to fetal blood, blood with elevated O₂, and blood that had P_O2 and P_CO2 values similar to arterial blood of newborn animals. Neither increased O₂ nor decreased CO₂ in the blood perfusing the lungs stimulated pulmonary prostacyclin synthesis. We conclude that the mechanism responsible for the stimulation of pulmonary prostacyclin with the onset of ventilation at birth is tissue stress during establishment of gaseous ventilation and rhythmic ventilation.     

A theoretical model for studying the rate of oxygenation of blood in pulmonary capillaries

A mathematical analysis of the process of gas exchange in the lung is presented taking into account the transport mechanisms of molecular diffusion, convection and facilitated diffusion of the species due to haemoglobin. Since the rate at which blood gets oxygenated in the pulmonary capillaries is very fast, it is difficult to set up an experimental study to determine the effects of various parameters on equilibration rate. The proposed study is aimed at determining the effects of various physiological parameters on equilibration rate in pathological conditions.Among the significant results are that 1. dissolved oxygen takes longer to achieve equilibration across the pulmonary membrane and carbon dioxide attains equilibration faster, 2. the equilibration length increases with increase in blood velocity, haemoglobin concentration, calibre of pulmonary capillaries and fall in alveolar PO₂, 3. the alveolar PCO₂ and forward and backward reaction rates of haemoglobin with CO₂ do not materially affect the equilibration rate or length. 4. At complete equilibration, by the end of the pulmonary capillary 92% of the total haemoglobin has combined with oxygen and 8% free pigment is left which is present as carbamino haemoglobin, met haemoglobin, carboxy haemoglobin etc.These results are of some importance for anaemic conditions, muscular exercise, meditation, altitude physiology, hypo-ventilation, hyperventilation, etc.Symbols H⁺ hydrogen ion - O₂ oxygen - CO₂ carbondioxide - HbO₂ oxyhaemoglobin - HbCO₂ carbaminohaemoglobin - PO₂ partial pressure of O₂ - PCO₂ partial pressure of CO₂ - PaO₂ O₂ tension in arterial blood - PaCO₂ CO₂ tension in arterial blood - k₁ forward rate constant for Eq. (1) - k₂ backward rate constant for Eq. (1) - m₁ forward rate constant for Eq. (2) - m₂ backward rate constant for Eq. (2) - k equilibration rate - a radius of the capillary - Q velocity of blood - L length of the capillary - D₀ diffusion coefficient of O₂ - D_c diffusion coefficient of CO₂ - D_H diffusion coefficient of Hb - H total haemoglobin concentration - A matrix - c₁ concentration of dissolved O₂ in blood - c₂ concentration of HbO₂ in blood - c₃ concentration of dissolved CO₂ in blood - c₄ concentration of HbCO₂ in blood - c₅ concentration of haemoglobin - c1alv concentration of O₂ in the alveolar region - c_3alv concentration of CO₂ in the alveolar region - c_iven concentration of the ith species in venous blood - c_iart concentrations of the ith species in arterial blood - F _is concentrations of the species in dimensionless form - J₀, I₀ Bessel's functions - P_alvO₂ tension of O₂ in alveolar region - P_alvCO₂ tension of CO₂ in alveolar region.     

Steady-state maternal and fetal plasma concentrations of glyceryl trinitrate (GTN) in the preterm sheep

The administration of glyceryl trinitrate (GTN; nitroglycerin) is increasing during preterm pregnancies, yet its disposition and, importantly, the extent of fetal exposure remain to be elucidated. When used as a tocolytic (pharmacological agent that stops uterine contractions), it is administered transdermally (24-48 h). Here, we quantified the maternal and fetal steady-state plasma concentrations of maternal intravenous GTN in preterm sheep and continuously monitored maternal and fetal vascular parameters to observe possible dose-dependent vascular effects. Preterm (120 days gestation) pregnant sheep (n = 6) were instrumented with maternal femoral arterial (MA) and venous (MV) and fetal femoral arterial (FA) and umbilical venous (UV) polyethylene blood-sampling catheters. During maternal GTN infusion (3.0 micro g.kg-1.min-1, 60-min duration) the steady-state GTN concentrations ([GTN]) were as follows: MA, 98.6 +/- 9.0 nM; UV, 17.4 +/- 7.6 nM; and FA, <5 nM. There were no changes in maternal and fetal mean arterial pressure and heart rate or in uterine activity. Overall, the steady-state [GTN] was established by 5 min, and the UV/MA ratio of [GTN] was 0.18. The FA [GTN] (<5 nM) indicates that the fetus cleared essentially all GTN in the UV, and the maternal and fetal heart rate and mean arterial pressure appear to be independent of maternal GTN infusion.     

Effects of posture, hypotension and locally applied vasoconstriction on the middle ear microcirculation in anaesthetized humans

Studies by laser-Doppler flowmetry of middle ear microcirculation changes induced by physical and chemical stimuli in the animal have only recently been made. This prospective study, performed in humans, was designed to compare the effects of a postural manoeuvre (headup tilt 30°), hypotension and locally applied vasoconstriction on middle ear blood flow during anaesthesia. Circulatory changes provoked by a headup tilt of 30°, and successive intravenous boluses of potent vasodilators, were compared with circulatory changes provoked by locally applied adrenaline, in ten healthy patients in good physical states undergoing middle ear surgical repair. Heart rate and direct arterial pressure were continuously recorded via a radial artery cannula. Middle ear blood flow was continuously recorded via a laser-Doppler probe placed on the promontorium cavi tympani. Metabolic parameters (partial pressure of O₂ and CO₂ in arterial blood, pH, arterial lactate concentrations) and arterial concentrations of propofol were measured just before and just after the experiment. Headup tilt did not modify heart rate, mean arterial pressure or middle ear blood flow. Vasodilators (nicardipine, nitroprusside, nitroglycerin) provoked a fall in arterial pressure (P<0.0001,P<0.0001,P<0.019, respectively), but did not induce any significant variations in heart rate; variations occurred in middle ear blood flow (P>0.05, not significant) which were different according to patients and agents. Locally applied adrenaline provoked a fall in the middle ear blood flow (P<0.0012), with no effect on heart rate and arterial pressure. There were no significant changes in metabolic values, or propofol serum concentrations. The behaviour of the middle ear blood flow submitted to hypotension, posture, or to vasoconstriction could be related to counteracting regulatory responses and/or to direct vascular effects.     

Oxygen exchange mechanisms in the human placenta: mathematical modelling and simulation

An exact knowledge of the human fetus's respiratory mechanisms is still lacking; in particular, the role of human placental anatomy in oxygen exchange has not yet been studied satisfactorily. In this paper, a mathematical model of placenta as O₂ exchanger between maternal and fetal blood was developed; it led to the solution of equations based upon diffusion laws and the haemoglobin dissociation curve. Particular care was taken to represent the regimen of laminar motion or whirling into the capillaries. Theoretical results were compared, under physiological conditions, with clinical data relating to fetal oxygenated blood pO₂ during the second half of gestation (20th–38th weeks), and a theoretical confirmation of the decreasing effectiveness of placental O₂ exchange during gestation was found. The result was able to describe oxygen exchange during a period in which clinical data are scanty (23rd–30th weeks). The effects of some pathological events on O₂ exchange were then simulated. Model parameters were changed to simulate the effects on oxygen exchange of some typical pathological variations of placental anatomical features: exchange surface thickness and capillary length. The curves obtained for different gestational ages can easily be correlated with echographic measures of placental volume and dimensions of placental capillaries. The results also show that the human placenta is more sensitive to pathologies when it is young than at term of gestation.     

Glutathione oxidation correlates with one-lung ventilation time and PO2/FiO2 ratio during pulmonary lobectomy

Objectives: During lung lobectomy, the operated lung completely collapses with simultaneous hypoxic pulmonary vasoconstriction, followed by expansion and reperfusion. Here, we investigated glutathione oxidation and lipoperoxidation in patients undergoing lung lobectomy, during one-lung ventilation (OLV) and after resuming two-lung ventilation (TLV), and examined the relationship with OLV duration.

Methods: We performed a single-centre, observational, prospective study in 32 patients undergoing lung lobectomy. Blood samples were collected at five time-points: T0, pre-operatively; T1, during OLV, 5 minutes before resuming TLV; and T2, T3, and T4, respectively, 5, 60, and 180 minutes after resuming TLV. Samples were tested for reduced glutathione (GSH), oxidized glutathione (GSSG), glutathione redox potential, and malondialdehyde (MDA).

Results: GSSG and MDA blood levels increased at T1, and increased further at T2. OLV duration directly correlated with marker levels at T1 and T2. Blood levels of GSH and glutathione redox potential decreased at T1?T3. GSSG, oxidized glutathione/total glutathione ratio, and MDA levels were inversely correlated with arterial blood PO₂/FiO₂ at T1 and T2.

Discussion: During lung lobectomy and OLV, glutathione oxidation, and lipoperoxidation marker blood levels increase, with further increases after resuming TLV. Oxidative stress degree was directly correlated with OLV duration, and inversely correlated with arterial blood PO₂/FiO₂.     

Influence of initial respiratory status on the short-and long-term activity of the trout red blood cell β-adrenergic Na+/H+ exchanger

The effects of ambient O₂ partial pressure and CO₂ partial pressure on the intensity of rainbow trout (Oncorhynchus mykiss) red blood cell -adrenergic Na⁺/H⁺ exchange were investigated. This was accomplished in vitro by continuously monitoring whole blood extracellular pH, partial pressures of O₂ and CO₂ and by measuring red blood cell water content and Na⁺ concentration before and 30 min after the addition of a catecholamine mixture (final nominal concentrations: 250 nmol·l^-1 adrenaline and 20 nmol·l^-1 noradrenaline). The experiments were performed under six different initial conditions combining two ambient partial pressures of CO₂ (1.50 and 6.75 torr) and three ambient partial pressures of O₂ (15, 30 and 150 torr). The activation of red blood cell Na⁺/H⁺ exchange (as indicated by marked reductions of whole blood pH) was followed by transient reductions in blood partial pressures of CO₂ and O₂ (2 min) resulting from the shift of the CO₂/HCO₃ ^- equilibrium within the cell and the subsequent binding of O₂ to the haemoglobin. The initial reduction in blood CO₂ partial pressure was followed by a rise reflecting the titration of plasma HCO₃ ^- by extruded H⁺. At low partial pressure of CO₂ (1.50 torr) there was a pronounced stimulatory effect of hypoxia on the initial intensity of the extracellular acidification (5 min), whereas at high CO₂ partial pressure (6.75 torr) hypoxia actually lowered the extent of the initial acidification. In all cases, Na⁺/H⁺ exchange activation was accompanied by increases in cell water content and red blood cell Na⁺ levles when measured 30 min after addition of catecholamines. Both hypercapnia and hypoxia increased the magnitude of these changes although the largest changes in cell water content and Na⁺ levels were observed under hypercapnic conditions. Thus, the long-term activity (as determined by measuring cell water and Na⁺ levels) of the Na⁺/H⁺ exchanger was enhanced both by hypercapnia and hypoxia regardless of the initial CO₂ partial pressure. The initial activity (5 min), on the other hand, although stimulated by hypercapnia was influenced by hypoxia in opposing directions depending upon the initial CO₂ partial pressure of the blood.Abbreviations RBC red blood cell(s) - Hb haemoglobin - pHe extracellular pH - P _bCO₂ blood partial pressure of CO₂ - P _bO₂ blood partial pressure of O₂     

Rapid vasoregulatory mechanisms in exercising human skeletal muscle: dynamic response to repeated changes in contraction intensity

We tested the hypothesis that vasoregulatory mechanisms exist in humans that can rapidly adjust muscle blood flow to repeated increases and decreases in exercise intensity. Six men and seven women (age, 24.4+/-1.3 yr) performed continuous dynamic forearm handgrip contractions (1- to 2-s contraction-to-relaxation duty cycle) during repeated step increases and decreases in contraction intensity. Three step change oscillation protocols were examined: Slow (7 contractions per contraction intensityx10 steps); Fast (2 contractions per contraction intensityx15 steps); and Very Fast (1 contraction per contraction intensityx15 steps). Forearm blood flow (FBF; Doppler and echo ultrasonography), heart rate (ECG), and mean arterial pressure (arterial tonometry) were examined for the equivalent of a cardiac cycle during each relaxation phase (FBFrelax). Mean arterial pressure and heart rate did not change during repeated step changes (P=0.352 and P=0.190). For both Slow and Fast conditions, relaxation phase FBFrelax adjusted immediately and repeatedly to both increases and decreases in contraction intensity, and the magnitude and time course of FBFrelax changes were virtually identical. For the Very Fast condition, FBFrelax increased with the first contraction and thereafter slowly increased over the course of repeated contraction intensity oscillations. We conclude that vasoregulatory mechanisms exist in human skeletal muscle that are capable of rapidly and repeatedly adjusting muscle blood flow with ongoing step changes in contraction intensity. Importantly, they demonstrate symmetry in response magnitude and time course with increasing versus decreasing contraction intensity but cannot adjust to very fast exercise intensity oscillations.     

Pre-and post-branchial blood respiratory status during acute hypercapnia or hypoxia in rainbow trout,Oncorhynchus mykiss

Simultaneous venous (pre-branchial) and arterial (post-branchial) extracorporeal blood circulations were utilized to monitor continuously the rapid and progressive effects of acute environmental hypercapnia (water partial pressure of CO₂ 4.8±0.2 torr) or hypoxia (water partial pressure of O₂ 25±2 torr) on oxygen and carbon dioxide tensions and pH in the blood of rainbow trout (Oncorhynchus mykiss). During hypercapnia, the CO₂ tension in the arterial blood increased from 1.7±0.1 to 6.2±0.2 torr within 20 min and this was associated with a decrease of arterial extracellular pH from 7.95±0.03 to 7.38±0.03; the acid-base status of the mixed venous blood changed in a similar fashion. The decrease in blood pH in vivo was greater than in blood equilibrated in vitro with a similar CO₂ tension indicating a significant metabolic component to the acidosis in vivo. Under normocapnic conditions, venous blood CO₂ tension was slightly higher than arterial blood CO₂ tension difference was abolished or reversed during the initial 25 min of hypercapnia indicating that CO₂ was absorbed from the water during this period. Arterial O₂ tension remained constant during hypercapnia; however, venous blood O₂ tension decreased significantly (from 22.0±2.6 to 9.0±1.0 torr) during the initial 10 min. Hypercapnia elicited the release of catecholamines (adrenaline and noradrenaline) into the blood. The adrenaline concentration increased from 6±3 to 418±141 nmol · l^-1 within 25 min; noradrenaline concentration increased from 3±0.5 to 50±21 nmol · l^-1 within 15 min. During hypoxia arterial blood O₂ tension declined progressively from 108.4±9.9 to 12.8±1.7 torr within 30 min. Venous blood O₂ tension initially was stable but then decreased abruptly as catecholamines were released into the circulation. The release of catecholamines occurred concomitantly with a sudden metabolic acidosis in both blood compartments and a rise in CO₂ tension in the mixed venous blood only.Abbreviations CCO₂ plasmatotal carbondioxide - CtO₂ blood oxygen content - PO₂ partial pressure of oxygen - PCO₂ partial pressure of carbon dioxide - PaO₂ arterial bloodPO₂ - PaCO₂ arterial bloodPCO₂ - PvCO₂ venous bloodPCO₂ - PwO₂ waterPO₂ - PwCO₂ waterPCO₂ - Hb haemoglobin - SHbO₂ haemoglobin oxygen saturation - HPLC high-performance liquid chromatography - rbc red blood cell(s) - Hct haematocrit     

Cardio-respiratory effects of chloramine-T exposure in rainbow trout

In order to establish whether the blood gas respiratory disturbances noted with exposure to chloramine-T are due to differences in the rates of uptake of O₂ and excretion of CO₂ or gill blood flow, adult rainbow trout (Oncorhynchus mykiss) were fitted with dorsal aorta and bulbus arteriosus catheters to facilitate blood pressure recordings, an ultrasonic blood flow probe and opercular impedance electrodes. Fish received either a 45-min static exposure to 9 mg l⁻¹ chloramine-T or tap water (control) and continuous recordings of blood pressure, and ventilation frequency and amplitude were made. Pre- and post-exposure arterial and venous blood samples were taken and analyzed for O₂ and CO₂ content, hemoglobin concentration and hematocrit. Chloramine-T exposure had no effect on any of the continuously recorded parameters. However, individual measurements (made immediately prior to and following exposure) of cardiac output and O₂ uptake rates increased significantly following exposure to chloramine-T compared to before exposure. CO₂ excretion rates were unaffected by chloramine-T exposure. Calculation of the perfusion convection requirement showed a significant increase for CO₂ but not for O₂. It was concluded that increases in O₂ uptake resulted from increased cardiac output but that CO₂ excretion, a diffusion-limited process, was not increased due to additional diffusive limitations caused by the irritant effect of chloramine-T.     

Exercise responses in pregnant sheep: blood gases, temperatures, and fetal cardiovascular system

In an effort to examine the effects of maternal exercise on the fetus we measured maternal and fetal temperatures and blood gases and calculated uterine O2 consumption in response to three different treadmill exercise regimens in 12 chronically catheterized near-term sheep. We also measured fetal catecholamine concentrations, heart rate, blood pressure, cardiac output, blood flow distribution, blood volume, and placental diffusing capacity. Maternal and fetal temperatures increased a mean maximum of 1.5 +/- 0.5 (SE) and 1.3 +/- 0.1 degrees C, respectively. We corrected maternal and fetal blood gas values for the temperatures in vivo. Maternal arterial partial pressure of O2 (PO2), near exhaustion during prolonged (40 min) exercise at 70% maximal O2 consumption, increased 13% to a maximum of 116.7 +/- 4.0 Torr, whereas partial pressure of CO2 (PCO2) decreased by 28% to 27.6 +/- 2.2 Torr. Fetal arterial PO2 decreased 11% to a minimum of 23.2 +/- 1.6 Torr, O2 content by 26% to 4.3 +/- 0.6 ml X dl -1, PCO2 by 8% to 49.6 +/- 3.2 Torr, but pH did not change significantly. Recovery was virtually complete within 20 min. During exercise total uterine O2 consumption was maintained despite the reduction in uterine blood flow because of hemoconcentration and increased O2 extraction. The decrease of 3 Torr in fetal arterial PO2 and 1.5 ml X dl -1 in O2 content did not result in major cardiovascular changes or catecholamine release. These findings suggest that maternal exercise does not represent a major stressful or hypoxic event to the fetus.     

Effect of electrical stimulation of leg muscles on physiological responses during arm-cranking exercise in healthy men

The purpose of this study was to investigate the hypothesis that changes in physiological responses during arm-cranking exercise using electrical stimulation of the leg muscles (ACE-ES) compared to arm-cranking exercise alone (ACE) in able-bodied subjects (ABS) are based on an increase in active muscle mass rather than the enhancing effect of the leg muscle pump. In ABS the sympathetic nervous system induced vasoconstriction and activity of the leg muscle pump are intact, therefore, a normal redistribution of blood takes place during exercise. Consequently, ES should have no additional effect on the redistribution of blood in these ABS during exercise and, thus, changes in physiological responses will be based on an increase in active muscle mass. A group of 11 ABS performed three maximal arm-cranking tests. In the first test peak power output (PO _peak) was determined. The other tests were both submaximal and maximal ACE, once with ACE-ES and once with ACE. The PO _peak was not significantly different between ACE-ES and ACE. Oxygen uptake (O₂) increased significantly during ACE-ES compared to ACE. Cardiac output (), stroke volume (SV), heart rate and ventilation were not significantly different during ACE-ES compared to ACE. Respiratory exchange ratios were significantly lower during ACE-ES compared to ACE at 60% PO _peak and at maximal exercise. In conclusion, ACE-ES caused significant increases in O₂ with a lack of elevation in and SV during submaximal and maximal exercise in ABS. The results of this study suggest that changes in physiological responses during ACE-ES are based on an increase in the active muscle mass rather than stimulation of the leg muscle pump. Accepted: 6 August 1996     

Acute Pancreatitis and Diabetic Ketoacidosis in Accidental Hypothermia and Hypothermic Myxoedema

Serial serum amylase and blood glucose levels were measured in 68 hypothermic (rectal temperature 35°C or less) patients, including 15 who had hypothermic myxoedema (serum protein bound iodine 3·5 μg/100 ml or less). Raised amylase levels were found in 34 patients and probably reflected a mild acute pancreatitis. The high amylase levels correlated with low arterial PO₂ levels and significantly with high arterial PCO₂ levels and the base deficit but not with the severity or duration of the hypothermia. The acute pancreatitis does not explain why hypothermic patients with myxoedema have a poorer prognosis than those who are euthyroid. The pancreatitis occasionally contributed to the development, sometimes delayed, of diabetic ketoacidosis, blood glucose levels of over 120 mg/100 ml being found in 20 patients. There was a significant correlation between the raised serum amylase levels and the hyperglycaemia. Hypoglycaemia, sometimes profound, was found in 12 patients.