Influence of noninvasive peripheral arterial blood pressure measurements on assessment of dynamic cerebral autoregulation.

Assessment of dynamic cerebral autoregulation (CA) requires continuous recording of arterial blood pressure (ABP). In humans, noninvasive ABP recordings with the Finapres device have often been used for this purpose. We compared estimates of dynamic CA derived from Finapres with those from invasive recordings in the aorta. Measurements of finger noninvasive ABP (Finapres), intra-aortic ABP (Millar catheter), surface ECG, transcutaneous CO2, and bilateral cerebral blood flow velocity (CBFV) in the middle cerebral arteries were simultaneously and continuously recorded in 27 patients scheduled for percutaneous coronary interventions. Phase, gain, coherence, and CBFV step response from both the Finapres and intra-arterial catheter were estimated by transfer function analysis. A dynamic autoregulation index (ARI) was also calculated. For both hemispheres, the ARI index and the CBFV step response recovery at 4 s were significantly greater for the Finapres-derived estimates than for the values obtained from aortic pressure. The transfer function gain for frequencies <0.1 Hz was significantly smaller for the Finapres estimates. The phase frequency response was significantly greater for the Finapres estimates at frequencies >0.1 Hz, but not at lower frequencies. The Finapres gives higher values for the efficiency of dynamic CA compared with values derived from aortic pressure measurements, as indicated by biases in the ARI index, CBFV step response, gain, and phase. Despite the significance of these biases, their relatively small amplitude indicates a good level of agreement between indexes of CA derived from the Finapres compared with corresponding estimates obtained from invasive measurements of aortic ABP.     

Identification of Human Vital Functions Directly Relevant to the Respiratory System Based on the Cardiac and Acoustic Parameters and Random Forest

Regarding sleep research, polysomnography (PSG) also called a sleep study, is a gold standard. It incorporates brain waves, the oxygen level in the blood, heart rate and breathing, and leg movement recordings. PSG is a complicated and expensive laboratory-based procedure, usually done in hospitals or special sleep center. In this study, an alternative technique for Sleep-Related Breathing Disorders (SRBD) based on selected cardiac and acoustic parameters and the Random Forest (RF) has been studied. A system dedicated to the detection of simultaneously acquired ECG and acoustic signals, which are collected during sleep at home environment is proposed. Results obtained indicate that classification and regression tree models such as RF are appropriate for the evaluation of sleep disorders like SRBD. The best identification of sleep irregularities at level 89.00 percent for the raw database was obtained. Thus, statistical predictive models allow identification of breathing events with high levels of sensitivity and specificity, providing an inexpensive and accurate diagnosis.     

Individual variability of cardiovascular reactivity during protective cardiac reflex in humans

Fail of fast recovering to normal state after aversive event is the key feature of individual intolerance to emotional stress. Within the framework of this idea, dynamics of the arterial blood pressure reactivity was studied studied using defensive reaction of the cardiac defense response elicited by strong aversive acoustic stimuli. Dynamical patterns of cardiovascular responses observed in this reaction makes made it possible to perform affective chronometry of defensive arousal. Healthy male volunteers with normal arterial blood pressure and patients with firstly diagnosed and untreated essential hypertension were studied. The beat-by-beat dynamics of blood pressure values were registered by means of finger-cuff Finapres technology. It was shown that among healthy individuals with normal resting blood pressure values hyperreactive persons with delayed late systolic and diastolic blood pressure increases ocurred. It was suggested that similiarity of delayed pressor effects ofhypereactive healthy individuals and those of hypertension patients incate a high risk of essential hypertension in highly reactive individuals.     

松龄血脉康对1级高血压合并睡眠障碍患者的临床疗效

目的:探讨松龄血脉康对1级高血压合并睡眠障碍患者生活质量及临床疗效的影响。方法:收集我院收治的150例1级高血压合并睡眠障碍患者,随机分为实验组和对照组,每组75例。对照组患者给予硝苯地平缓释片并结合低盐饮食,减少脂肪摄入,减轻体重,增加体育活动等。实验组患者在对照组患者基础上给予松龄血脉康胶囊。观察并比较两组患者的治疗前后血压、生活质量水平以及患者睡眠障碍、高血压的临床疗效。结果:与治疗前相比,两组患者治疗后收缩压、舒张压水平均下降,生活质量评分均升高,差异具有统计学意义(P0.05);与对照组相比,实验组患者收缩压、舒张压水平较低,生活质量评分、睡眠障碍以及高血压的治疗有效率较高,差异具有统计学意义(P0.05)。结论:松龄血脉康能够降低1级高血压合并睡眠障碍患者血压水平,提高其生活质量,提高治疗效果。     

Method for measuring respiration in sleep: capnography for determining ventilation]

Ventilation serves the exchange of gases between the organism and the environment. Oxygen uptake and CO2 elimination are controlled by feedback loops, that keep fluctuations in arterial CO2 pressure (PaCO2) within narrow limits Disorders in the central regulation of breathing, or impairment of the respiratory apparatus, may result in a mismatch between metabolic CO2 production and ventilatory CO2, elimination and thus in fluctuations in the PaCO2: inappropriately increased ventilation (hyperventilation) causes hypocapnia, and reduced ventilation (hypoventilation) causes hypercapnia. In order to detect such disorders during sleep, PCO2 measurement is of great importance, but direct and continuous measurement of the PaCO2 is invasive and thus unsuitable in the clinical setting. An alternative is capnography, the continuous measurement of PCO2 in inhaled and exhaled air on the basis of ultrared light absorption. This paper reviews the method, its features and limitations, and the possibilities of improving capnography to better detect sleep-related breathing disorders. In addition, data obtained from 57 patients with predominantly normal lung function, but suspected sleep disordered breathing are presented. Simultaneous measurements of capnography PETCO2) and capillary PaCO2 revealed a PETCO2 difference of +0.63 +/- 3.3 (SD) Torr. PaCO2 (38.8 +/- 4.1 Torr) and PETCO2 (38.1 +/- 4.3 Torr) were not significantly different with a correlation coefficient of r = 0.68 (p < 0.001). Thus 46% of the variation in PETCO2 was explained by changes in PaCO2. Currently the literature contains few further data on capnography during sleep. It is concluded that, provided the limitations of the method are respected and comparison with the PETCO2 is made, capnography may be a useful, noninvasive and continuous measuring method for assessing ventilation during sleep in patients with suspected sleep related breathing disorders.     

Altered Orcadian Rhythms of Blood Pressure and Heart Rate in Non-Hemodialysis Chronic Renal Failure

The extended use of ambulatory monitoring has permitted the identification of many conditions in which the circadian rhythm of blood pressure is altered. The common denominator seems to be an impairment of the autonomic nervous system function. We examined whether the circadian blood pressure rhythm is altered in chronic renal failure (where autonomic dysfunction is usually present) by using a standardized chronobiological inferential statistical method in hospitalized subjects. For this purpose, a group of 30 non-hemodialysis hypertensive patients with chronic renal failure was compared with a second group of 30 patients affected by uncomplicated mild-to-moderate essential hypertension. The two groups were matched by age, sex and circadian mesors of blood pressure. Diet, meal times, sleep and activity logs were standardized. Blood pressure and heart rate recordings were obtained by using an automatic oscillometric recorder and subsequently analyzed according to the cosinor method. A mean circadian rhythm of blood pressure was documented in both groups, but while the mean acrophases occurred between 2 and 3 p.m. in essential hypertension, in renal failure they were between 11 p.m. and midnight for blood pressure and around 7 p.m. for heart rate. In addition, the mean circadian amplitudes were significantly lower in renal failure, while the mean circadian mesor of heart rate was significantly higher. Our data demonstrate that the circadian rhythms of blood pressure and heart rate are altered also in hypertension due to chronic renal failure.     

Altered Orcadian Rhythms of Blood Pressure and Heart Rate in Non-Hemodialysis Chronic Renal Failure

The extended use of ambulatory monitoring has permitted the identification of many conditions in which the circadian rhythm of blood pressure is altered. The common denominator seems to be an impairment of the autonomic nervous system function. We examined whether the circadian blood pressure rhythm is altered in chronic renal failure (where autonomic dysfunction is usually present) by using a standardized chronobiological inferential statistical method in hospitalized subjects. For this purpose, a group of 30 non-hemodialysis hypertensive patients with chronic renal failure was compared with a second group of 30 patients affected by uncomplicated mild-to-moderate essential hypertension. The two groups were matched by age, sex and circadian mesors of blood pressure. Diet, meal times, sleep and activity logs were standardized. Blood pressure and heart rate recordings were obtained by using an automatic oscillometric recorder and subsequently analyzed according to the cosinor method. A mean circadian rhythm of blood pressure was documented in both groups, but while the mean acrophases occurred between 2 and 3 p.m. in essential hypertension, in renal failure they were between 11 p.m. and midnight for blood pressure and around 7 p.m. for heart rate. In addition, the mean circadian amplitudes were significantly lower in renal failure, while the mean circadian mesor of heart rate was significantly higher. Our data demonstrate that the circadian rhythms of blood pressure and heart rate are altered also in hypertension due to chronic renal failure.     

Arousal and cardiopulmonary responses to hyperoxic hypercapnia in lambs

Experiments were done to investigate the arousal and cardiopulmonary responses to hyperoxic hypercapnia in 8 lambs. Each lamb was anaesthetized and instrumented for recordings of electrocorticogram, electro-oculogram, nuchal and diaphragm electromyograms and measurements of arterial blood pressure and haemoglobin oxygen saturation. No sooner than 3 days after surgery, measurements were made in quiet sleep and active sleep during control periods when the animal was breathing 21% oxygen and during experimental periods of hyperoxic hypercapnia when the animal was breathing 10% carbon dioxide and 30% oxygen. Hyperoxic hypercapnia was terminated during each epoch by returning the inspired gas mixture to 21% oxygen once the animal aroused from sleep. Arousal occurred from both sleep states during hyperoxic hypercapnia but was delayed in active sleep compared to quiet sleep (active sleep 58 +/- 17 s; quiet sleep 21 +/- 10 s; mean +/- 1SD). There were no significant changes in heart rate or blood pressure during hyperoxic hypercapnia before arousal. However, respiratory rate and diaphragm electrical activity did increase during hyperoxic hypercapnia before arousal. Thus, our data provide evidence that hypercapnia can initiate arousal from sleep in young lambs. The mechanisms responsible for this response are yet to be determined.     

Is pulse transit time useful in differentiating respiratory events for patients with a sleep breathing disorder? A pilot study

Variation of inspiratory effort in sleep disordered breathing induces the oscillation in blood pressure, which corresponds inversely to pulse transit time (PTT). This study evaluated the feasibility of PTT as a visual parameter for differentiating respiratory events in patients with a sleep breathing disorder. Sixteen patients who complained of snoring and sleep apnea were booked into the study. Polysomnographic data of Zopiclone induced daytime sleep were analyzed, PTT and intraesophageal pressure (Peso) were assessed for each respiratory event. With respect to Peso, the total accuracy of PTT was 51.8% for 1266 events. The relatively high coincidence rate could be observed in obstructive events (57.1%), with crescendo Peso pattern (71.5%), in lateral position (82.2%). Pulse transit time oscillation could only partly reflect respiratory rhythm to some degree (56.5%). Absolute PTT value presented a poor relationship with respiratory effort. Pulse transit time coincided well with crescendo Peso in lateral position for obstructive events. Swings in PTT could only partly fit respiratory wave data. Absolute PTT value and its change could not reflect respiratory effort. Although PTT is a non-invasive and convenient way for assessing inspiratory effort, its variable sensitivity to different events, respiratory patterns, positions, different patients and other situations, limit its feasibility. Further work is required.

     

Circadian variations of catecholamines and blood pressure in patients with pseudohypoparathyroidism and hypertension

The relationship between 24-h recumbent blood pressure levels and secretory patterns of catecholamines was investigated in 4 patients with pseudohypoparathyroidism (PsHP) and hypertension and in 9 patients with essential hypertension. A clear circadian rhythm of blood pressure and catecholamines was documented in both groups with lowest levels of blood pressures and catecholamines occurring during sleep. During the 24-h period of recumbency mean arterial blood pressure (MAP) was correlated (r = 0.63, p less than or equal to 0.01) with plasma norepinephrine (N) in the patients with essential hypertension, but this correlation was weaker in patients with PsHP (r = 0.38, p less than or equal to 0.05). MAP was more closely related to plasma epinephrine (E) (r = 0.62, p less than or equal to 0.01) than to plasma NE in patients with PsHP. Plasma NE and E levels were considerably lower in patients with PsHP than in patients with essential hypertension throughout the 24-h recumbent period. The sleep-related decline in blood pressure and NE was less than in patients with essential hypertension. These results suggest that while the sympathetic nervous system may have a role in hour-to-hour maintenance of blood pressure in patients with PsHP and hypertension, it does not appear to be responsible for the elevated arterial pressure in these patients. Factors other than those investigated, such as obesity, alterations in sodium homeostasis of refractoriness of the vascular smooth muscle to the vasodilatory effect of PTH may be involved in the pathogenesis of hypertension in PsHP.     

Influence of carotid-denervation on the arousal and cardiopulmonary responses to alveolar hypercapnia in lambs

Experiments were done on five lambs to determine if carotid-denervation influences the arousal and cardiopulmonary responses to alveolar hypercapnia during sleep. Each lamb was anaesthetized and instrumented for recordings of electrocorticogram, electro-oculogram, nuchal and diaphragm electromyograms and measurements of systemic arterial blood pressure and arterial haemoglobin oxygen saturation. The carotid chemoreceptors and baroreceptors were denervated, a tracheostomy was done and a fenestrated tracheostomy tube placed in the trachea so that the inspired gas mixture could be changed quickly. No sooner than three days after surgery, measurements were made in quiet sleep and active sleep during control periods when the animal was breathing room air and during experimental periods of alveolar hypercapnia when the lamb was breathing 10% carbon dioxide in air. Alveolar hypercapnia was terminated during an experimental period by changing the gas mixture back to room air once the animal aroused from sleep. If an animal did not arouse within 2 min, the gas mixture was changed back to room air. Arousal occurred during only 6 of 12 epochs in quiet sleep and during only 2 of 10 epochs in active sleep. These data provide evidence that the carotid chemoreceptors and/or carotid baroreceptors play a major role in causing arousal from sleep during alveolar hypercapnia in lambs.     

Cerebral pressure-flow relations in hypertensive elderly humans: transfer gain in different frequency domains.

The dynamics of the cerebral vascular response to blood pressure changes in hypertensive humans is poorly understood. Because cerebral blood flow is dependent on adequate perfusion pressure, it is important to understand the effect of hypertension on the transfer of pressure to flow in the cerebrovascular system of elderly people. Therefore, we examined the effect of spontaneous and induced blood pressure changes on beat-to-beat and within-beat cerebral blood flow in three groups of elderly people: normotensive, controlled hypertensive, and uncontrolled hypertensive subjects. Cerebral blood flow velocity (transcranial Doppler), blood pressure (Finapres), heart rate, and end-tidal CO(2) were measured during the transition from a sit to stand position. Transfer function gains relating blood pressure to cerebral blood flow velocity were assessed during steady-state sitting and standing. Cerebral blood flow regulation was preserved in all three groups by using changes in cerebrovascular resistance, transfer function gains, and the autoregulatory index as indexes of cerebral autoregulation. Hypertensive subjects demonstrated better attenuation of cerebral blood flow fluctuations in response to blood pressure changes both within the beat (i.e., lower gain at the cardiac frequency) and in the low-frequency range (autoregulatory, 0.03-0.07 Hz). Despite a better pressure autoregulatory response, hypertensive subjects demonstrated reduced reactivity to CO(2). Thus otherwise healthy hypertensive elderly subjects, whether controlled or uncontrolled with antihypertensive medication, retain the ability to maintain cerebral blood flow in the face of acute changes in perfusion pressure. Pressure regulation of cerebral blood flow is unrelated to cerebrovascular reactivity to CO(2).     

原发性高血压患者心率变异性及血压变异性与血管损害的相关性研究

目的:探讨原发性高血压患者心率变异性(HRV)及血压变异性(BPV)与血管损害的相关性。方法:选取2014年12月到2017年12月期间在我院接受治疗的原发性高血压患者94例,根据脉搏波传导速度(PWV)的不同分为对照组(60例)和血管受损组(34例)。比较两组患者的HRV、BPV指标,并分析PWV与HRV、BPV指标的相关性。结果:血管受损组的5 min心搏R-R间期平均值的标准差(SDANN)低于对照组,低频(LF)、高频(HF)、低高频之比(LF/HF)高于对照组,差异均有统计学意义(P0.05);血管受损组的24h平均收缩压(24h SBP)、24h平均脉压(24h PP)、白天平均收缩压(dSBP)、白天平均脉压(dPP)、夜间平均收缩压(nSBP)、夜间平均脉压(nPP)高于对照组,差异均有统计学意义(P0.05);PWV与LF、HF、LF/HF、24h SBP、24h PP、dSBP、dPP、nSBP、nPP均呈正相关(P0.05)。结论:原发性高血压患者部分HRV、BPV指标与PWV呈明显的相关性,说明HRV和BPV与患者的血管损害密切相关。     

Health effects of obstructive sleep apnoea and the effectiveness of continuous positive airways pressure: a systematic review of the research evidence.

OBJECTIVE: To examine the research evidence for the health consequences of obstructive sleep apnoea and the effectiveness of continuous positive airways pressure. DESIGN: A systematic review of published research, studies being identified by searching Medline (1966-96), Embase (1974-96), and CINAHL (Cumulative Index to Nursing and Allied Health Literature) (1982-95); scanning citations; and consulting experts. Studies in all languages were considered which either investigated the association between obstructive sleep apnoea in adults and key health outcomes or evaluated the effectiveness of treatment of obstructive sleep apnoea with continuous positive airways pressure in adults. MAIN OUTCOME MEASURES: Mortality, systematic hypertension, cardiac arrhythmias, ischaemic heart disease, left ventricular hypertrophy, pulmonary hypertension, stroke, vehicle accidents, measures of daytime sleepiness, and quality of life. RESULTS: 54 epidemiological studies examined the association between sleep apnoea and health related outcomes. Most were poorly designed and only weak or contradictory evidence was found of an association with cardiac arrhythmias, ischaemic heart disease, cardiac failure, systemic or pulmonary hypertension, and stroke. Evidence of a link with sleepiness and road traffic accidents was stronger but inconclusive. Only one small randomised controlled trial evaluated continuous positive airways pressure. Five non-randomised controlled trials and 38 uncontrolled trials were identified. Small changes in objectively measured daytime sleepiness were consistently found, but improvements in morbidity, mortality, and quality of life indicators were not adequately assessed. CONCLUSIONS: The relevance of sleep apnoea to public health has been exaggerated. The effectiveness of continuous positive airways pressure in improving health outcomes has been poorly evaluated. There is enough evidence suggesting benefit in reducing daytime sleepiness in some patients to warrant large randomised placebo controlled trials of continuous positive airways pressure versus an effective weight reduction programme and other interventions.     

Continuous and noninvasive recording of cardiovascular parameters with the Finapres finger cuff enhances undergraduate student understanding of physiology

The Finapres finger cuff recording system provides continuous calculations of beat-to-beat variations in cardiac output (CO), total peripheral resistance, heart rate (HR), and blood pressure (BP). This system is unique in that it allows experimental subjects to immediately, continuously, and noninvasively visualize changes in CO at rest and during exercise. This study provides evidence that using the Finapres system improves undergraduate student engagement, understanding, and learning of how the cardiovascular system responds to exercise. Second-year science students undertaking a physiology practical class in 2009 (n = 243) and 2010 (n = 263) used the Finapres system to record CO, BP, and HR during graded exercise on a cycle ergometer. Student experiences with the Finapres was evaluated with a survey (a 5-point scale from strongly disagree to strongly agree). This indicated that students appreciated the immediacy of the recordings (88% of students agreed or strongly agreed, average for 2009 and 2010), gained an understanding of how to record physiological data (84%), enjoyed the practical (81%), and would recommend the Finapres to other students (81%). To determine if the practical enhanced student learning of cardiovascular physiology, identical tests were given to the students at the beginning (pretest) and end (posttest) of the class. There was a significant improvement from the pretest to the posttest (4% in 2009 and 20% in 2010). In summary, the ability of the Finapres to continuously display CO, BP, and HR during experimental protocols provides students with immediate feedback and improves their understanding of cardiovascular physiology.     

The Relationship between CPAP Usage and Corneal Thickness

The purpose of this study was to determine whether there is a correlation between CPAP usage and corneal thickness in patients with sleep disordered breathing. Full-night polysomnography (PSG) recordings were collected. Ten patients had undergone PSG recordings with continuous positive airway pressure (CPAP), and seven patients had undergone PSG recordings without CPAP. We measured corneal thickness by ultrasonic pachymeter before sleep and ten minutes after waking. We also measured visual acuity with a routine ophthalmologic eye chart before and after sleep. We asked patients to fill out a post-sleep questionnaire to get their subjective opinions. In the without-CPAP group, corneal thickness increased significantly during sleep in both eyes (left, p = 0.0025; right, p<0.0001). In the with-CPAP group, corneal thickness did not increase significantly (p>0.05 for both left and right cornea). There was no significant difference in visual acuity tests (p>0.05 for both left and right eye) between the two groups. According to our results, there is a significant increase in corneal thickness in the without-CPAP group. Our data show that a low percentage of Rapid Eye Movement (REM) sleep may cause an increase in corneal thickness, which can indicate poor corneal oxygenation. In fact, many sleep-disordered breathing (SDB) patients have low REM. Since a contact lens may cause low corneal oxygenation, SDB patients with contact lenses should be monitored carefully for their corneal thickness.     

Nocturnal variations in human lower leg subcutaneous blood flow related to sleep stages.

Nocturnal subcutaneous adipose tissue blood flow rate was measured in the lower legs of 10 normal human subjects together with systemic arterial blood pressure, heart rate, and registration of sleep stages under ambulatory conditions. The 133Xe washout technique, portable CdTe(Cl) detectors, and a portable data storage unit were used for measurement of blood flow rates. The sleep recordings were performed with a portable computerized sleep analysis system. In accordance with the results of previous studies, a hyperemic blood flow rate phase (mean increase 140%) for 100 min was observed approximately 60 min after the subjects went to bed. The moment of onset of the hyperemic phase was closely related to the moment of onset of the first episode of deep sleep (stages 3 and 4). There was a significant (P < 0.01) overrepresentation of deep sleep in the hyperemic phase compared with adjacent phases, and rapid-eye-movement sleep predominantly occurred in the latter part of the night, when the subcutaneous blood flow rate was stable. The results of the present study are in accordance with current theories of the interrelationship between the thermoregulatory and the arousal state control systems and, thus, might suggest that the nightly subcutaneous hyperemia represents a thermoregulatory effector mechanism.     

No elevated plasma catecholamine levels during sleep in newly diagnosed, untreated hypertensives

The sympatho-adrenergic system is highly involved in regulating sleep, wake and arousal states, and abnormalities in this system are regarded as a key factor in the development and progression of arterial hypertension. While hypertension is associated with a hyperadrenergic state during wakefulness, the effect of hypertension on plasma-catecholamine levels during sleep is not yet known. Twelve young participants with newly diagnosed, untreated hypertension and twelve healthy controls slept for 7 hours in the sleep laboratory. Before and after sleep, subjects rested in a supine position for 3-h periods of wakefulness. We sampled blood at a fast rate (1/10 min) and monitored blood pressure and heart rate continuously. We show that plasma NE and E levels did not differ between hypertensives and normotensive during sleep as well as before and after sleep. Blood pressure was higher in hypertensives, reaching the largest group difference in the morning after sleep. Unlike in the normotensives, in the hypertensive participants the morning rise in blood pressure did not correlate with the rise in catecholamine levels at awakening. Our results suggest that hypertension in its early stages is not associated with a strong hyperadrenergic state during sleep. In showing a diminished control of blood pressure through sympatho-adrenergic signals in hypertensive participants, our data point towards a possible involvement of dysfunctional sleep-related blood pressure regulation in the development of hypertension.     

Baroreflex modulation of muscle sympathetic nerve activity during posthandgrip muscle ischemia in humans.

To identify whether muscle metaboreceptor stimulation alters baroreflex control of muscle sympathetic nerve activity (MSNA), MSNA, beat-by-beat arterial blood pressure (Finapres), and electrocardiogram were recorded in 11 healthy subjects in the supine position. Subjects performed 2 min of isometric handgrip exercise at 40% of maximal voluntary contraction followed by 2.5 min of posthandgrip muscle ischemia. During muscle ischemia, blood pressure was lowered and then raised by intravenous bolus infusions of sodium nitroprusside and phenylephrine HCl, respectively. The slope of the relationship between MSNA and diastolic blood pressure was more negative (P < 0.001) during posthandgrip muscle ischemia (-201.9 +/- 20.4 units. beat(-1). mmHg(-1)) when compared with control conditions (-142.7 +/- 17.3 units. beat(-1). mmHg(-1)). No significant change in the slope of the relationship between heart rate and systolic blood pressure was observed. However, both curves shifted during postexercise ischemia to accommodate the elevation in blood pressure and MSNA that occurs with this condition. These data suggest that the sensitivity of baroreflex modulation of MSNA is elevated by muscle metaboreceptor stimulation, whereas the sensitivity of baroreflex of modulate heart rate is unchanged during posthandgrip muscle ischemia.     

Respiratory, cardiovascular, and metabolic adjustments to hypoxemia during sleep in piglets

The influence of sleep on ventilation, metabolic rate, cardiovascular function, and regional distribution of blood flow during hypoxemia (PaO2 of 45-50 mm Hg (1 mm Hg = 133.3 Pa)) was studied in piglets at 6+/-1 and 34+/-5 days (mean+/-SD). Measurement of ventilation and metabolic rate was done in a metabolic chamber, and blood flow was measured using the microsphere technique. A subgroup of animals was instrumented for cardiac output measurement (dye-dilution technique) and continuous monitoring of the hemoglobin saturation in oxygen (SaO2). We found that although sleep did not influence the metabolic and cardiac output response to hypoxemia, it affected the ventilatory response as well as the brain and the respiratory muscle blood flows. During active sleep in the older animals, the ventilatory response to hypoxemia was smaller than in the other two states; marked drops in SaO2 occurred with changes in the breathing pattern; and that state was associated with the highest rate of brain blood flow. As well, age affected the ventilatory and metabolic response, but not the cardiovascular response to hypoxemia. The age-dependent ventilatory changes with hypoxemia (smaller ventilatory response in the young than in the older animals) were related to the different levels of oxygen consumption. In summary, active sleep was responsible for all the sleep-dependent changes in the response to a moderate degree of hypoxemia.