Twenty‐four‐hour non‐invasive monitoring of systemic haemodynamics and cerebral blood flow velocity in healthy humans

Acute short‐term changes in blood pressure (BP) and cardiac output (CO) affect cerebral blood flow (CBF) in healthy subjects. As yet, however, we do not know how spontaneous fluctuations in BP and CO influence cerebral circulation throughout 24 h. We performed simultaneous monitoring of BP, systemic haemodynamic parameters and blood flow velocity in the middle cerebral artery (MCAV) in seven healthy subjects during a 24‐h period. Finger BP was recorded continuously during 24 h by Portapres and bilateral MCAV was measured by transcranial Doppler (TCD) during the first 15 min of every hour. The subjects remained supine during TCD recordings and during the night, otherwise they were seated upright in bed. Stroke volume (SV), CO and total peripheral resistance (TPR) were determined by Modelflow analysis. The 15 min mean value of each parameter was assumed to represent the mean of the corresponding hour. There were no significant differences between right vs. left, nor between mean daytime vs. night time MCAV. Intrasubject comparison of the twenty‐four 15‐min MCAV recordings showed marked variations (P < 0.001). Within each single 15‐min recording period, however, MCAV was stable whereas BP showed significant short‐term variations (P < 0.01). A day–night difference in BP was only observed when daytime BP was evaluated from recordings in the seated position (P < 0.02), not in supine recordings. Throughout 24 h, MCAV was associated with SV and CO (P < 0.001), to a lesser extent with mean arterial pressure (MAP; P < 0.005), not with heart rate (HR) or TPR. These results indicate that in healthy subjects MCAV remains stable when measured under constant supine conditions but shows significant variations throughout 24 h because of activity. Moreover, changes in SV and CO, and to a lesser extent BP variations, affect MCAV throughout 24 h.     

Circadian systemic haemodynamics in borderline and mild hypertension.

Circadian variations in blood pressure (BP), stroke volume (SV), heart rate (HR), cardiac output (CO) and total peripheral resistance (TPR) were determined by a pulse contour method from the intra-arterial pulse wave in 32 normotensive (NT), 32 borderline hypertensive (BHT) and 31 hypertensive (HT) middle-aged men. Daytime averages were used as the reference levels. The nocturnal decrease in BP and HR were similar in the three groups. In the night, SV did not change in the NT group, but was increased in the BHT and HT groups. The nocturnal increase in SV may reflect reduced venous capacity causing increased cardiac filling. As a consequence of the difference in SV, the nocturnal CO fall was diminished in the HT group as compared with the NT group. Moreover, TPR had a tendency to decrease in the HT group, which may be considered as a baroreflex response to buffer the expected rise in BP. Five years later, 25 NT, 24 BHT and 19 HT subjects were reassessed using casual BP measurements. In the NT and BHT groups, six and 17 subjects, respectively, had progressed to hypertension. In a logistic regression model for those who became HT, the nocturnal increase in SV was a significant predictor for future hypertension. In conclusion, the results suggest that circadian systemic haemodynamics may be altered before BP is markedly elevated, and that haemodynamic studies might be useful in predicting the development of sustained hypertension.     

Renal and hormonal responses to isotonic saline infusion after 3 days' head-down tilt vs. supine and seated positions

AIM: The study aimed to determine whether prolonged exposure to simulated microgravity produces a level of thoracic volume receptor loading similar to that seen in the upright position or immediately after lying down. METHODS: We used a cross-over design to compare responses to a saline infusion in eight healthy subjects during a 4-day, -6 degree head-down tilt (HDT) and in the acute seated and acute supine positions. RESULTS: The first 24 h of HDT were associated with greater urinary excretion of water and sodium (UV, UNaV) than seated and acute supine [cumulative UV, 3035 +/- 219, 2311 +/- 156 (P < 0.05), and 2448 +/- 182 mL (P < 0.05), respectively; cumulative UNaV, 256 +/- 19, 180 +/- 11 (P < 0.05), and 189 +/- 15 mmol (P < 0.05), respectively]. Haemoglobin and haematocrit were increased after 24 h and plasma volume decreased after 48 h of HDT (P < 0.05). With prolongation of HDT, UV and UNaV returned near the baseline values, and plasma atrial natriuretic factor (ANF) and renin values returned to acute seated levels; in acute supine, ANF values were higher and renin lower than in the two other positions. After a 30-min infusion of 20 mL kg(-1) isotonic saline on the fourth HDT day or during acute seated or acute supine, sodium excretion within 4 h was similar during HDT and acute seated (83 +/- 6 and 84 +/- 9 mmol, respectively) and greater during supine (104 +/- 8 mmol, P < 0.05). The renin decrease was greater in HDT and seated than in supine. The plasma ANF increase was greater during HDT than during supine; during seated, plasma ANF was unchanged. CONCLUSION: These data suggest that, after 4 days of HDT, thoracic volume receptor loading returns to the same level as in the seated position, leading to blunted responses to volume expansion as compared with the acute supine position.     

Achieving haemodynamic baseline values with Finapres in elderly subjects during supine rest.

BACKGROUND: Clear guidelines for the resting time necessary to achieve stable blood pressure (BP) levels are scant in gerontology research. Therefore, we aimed to determine the minimum period required for obtaining haemodynamic baseline values in elderly subjects during supine rest. In addition, we evaluated the effect of cardiovascular morbidity, such as diastolic heart failure, and the effect of complex comorbidity of geriatric patients, on haemodynamic changes during supine rest. METHODS: A total of 17 healthy subjects, 18 heart failure patients with normal systolic function and 24 geriatric patients, aged 70 years and more, participated. After an overnight fast, changes in systolic BP (SBP), diastolic BP (DBP), heart rate (HR), and stroke volume (SV) were determined by Finapres beat-to-beat non-invasive BP monitoring during a 20-min supine rest. The procedure was repeated in the healthy subjects and geriatric patients on a second day. RESULTS: Complete BP stabilization was reached in each group within 5 min of supine rest, as SBP remained essentially unchanged and DBP did not change significantly anymore after the fourth minute. In the heart failure patients, HR decreased and SV increased until the twelfth minute of rest. The SBP, DBP, HR, and SV changes during supine rest showed good reproducibility. CONCLUSIONS: A span of 5 min of supine rest ensured achievement of reliable and reproducible baseline BP values by Finapres in elderly subjects. However, we recommend at least 12 min of rest to obtain full haemodynamic stability in elderly patients with diminished cardiac compliance and diastolic function.     

Effects of chemoreflexes on hyperthermic hyperventilation and cerebral blood velocity in resting heated humans

We tested the hypothesis that hyperthermic hyperventilation in part reflects enhanced chemoreceptor ventilatory O(2) drive, and that the resultant hypocapnia attenuates ventilatory responses and/or middle cerebral artery mean blood velocity (MCAV(mean)) in resting humans. Eleven healthy subjects were passively heated for 50-80 min, causing oesophageal temperature (T(oes)) to increase by 1.6 degrees C. During heating, minute ventilation increased (P < 0.05), while end-tidal CO(2) pressure (P(ET,CO(2))) and MCAV(mean) declined. A hyperoxia test in which three breaths of hyperoxic air were inspired was performed once before heating and three times during the heating. When we observed hypocapnia (P(ET,CO(2)) below 40 mmHg), P(ET,CO(2)) was restored to the eucapnic level by adding 100% CO(2) to the inspired air immediately before the last two tests. Minute ventilation was significantly reduced by hyperoxia, and that reduction gradually increased with increasing T(oes). However, the percentage decrease in from the normoxic level was small (20-29%) and unchanged during heating. When P(ET,CO(2)) was restored to eucapnic levels, was unchanged, but MCAV(mean) was partly restored to the level seen prior to heating (28.1% restoration at T(oes) 37.6 degrees C and 38.1% restoration at T(oes) 38.0 degrees C). These findings suggest that although hyperthermia increases chemoreceptor ventilatory O(2) drive in resting humans, the relative contribution of the chemoreceptor ventilatory O(2) drive to hyperthermic hyperventilation is small ( approximately 20%) and unaffected by increasing core temperature. Moreover, hypocapnia induced by hyperthermic hyperventilation reduces cerebral blood flow but not ventilatory responses.     

Development of methods to analyse transcranial Doppler ultrasound signals recorded in microgravity

During space flights, several clinical syndromes may be the result of changes in cerebral circulation. The purpose of the paper is to describe the development and initial evaluation of a system for recording, processing and displaying transcranial Doppler ultrasound (TCD) waveforms from the middle cerebral artery (MCA) in microgravity. Volunteers were repeatedly subjected to 15–20 s intervals of microgravity (‘near zero gravity’) during flights on the KC-135 military aircraft. Continuous TCD recordings from the MCA were stored on magnetic tape. The paper describes the system that was developed to digitise the Doppler ultrasound data and markers that corresponded to the various levels of microgravity, obtain the maximum and mean Doppler waveforms, identify the waveforms and quantify them. The results demonstrate the feasibility of making TCD recordings in a microgravity environment and illustrate excellent performance of the system and its ease of operation. Quantitative waveform analysis of the recordings from the first subject studied in the supine position showed statistically significant changes in MCA velocity waveforms during microgravity.     

大鼠脑血栓形成时心功能不全发生机制的探讨

以脑水含量、局部脑血液、全血血小板聚集、心输出量、每搏出量、心率、平均血压、外周总阻力及心、肝、脾。肾和肾上腺局部血流量为指标，探讨 光化学法诱导的实验性血栓形成性局部脑缺血时全血血小板功能改变对心功能的影响及其机理。结果表明，光化学反应后４小时，全血血小板聚集明显增强（Ｐ＜０．０１），ＣＯ、ＳＶ降低（Ｐ＜０．０５）；２４小时ｒＣＢＦ，ＣＯ，Ｓ及心肌ｒＢＦ均明显减少，ＴＰＲ及脑水含量明显增加（Ｐ＜     

G tolerance and the vasoconstrictor reserve

Purpose

Because leg arterial stiffness is higher in subjects with high G tolerance, we hypothesized that subjects with high G tolerance would have larger capacity for vasoconstriction.

Methods

Sixteen subjects, eight with high and eight with low G tolerance (H and L group, respectively), were exposed to a cold pressor test (CPT) in supine and upright posture. Heart rate (HR), mean arterial pressure (MAP) and cardiac output (CO) were measured, and total peripheral resistance (TPR) and stroke volume (SV) were calculated.

Results

In the supine position, CPT increased TPR more in the H group; 31 ± 18 % than in the L group; 11 ± 7 % (p < 0.05). The L group had larger increases in CO than the H group; 17 ± 16 vs. 3.4 ± 7 % (p = 0.06). In the upright position, the H group had a larger MAP response to CPT than the L group; 26 ± 14 vs. 14 ± 7 % (p = 0.06). The H group, but not the L group, had significant increases in TPR whereas the L group had significant increases in CO and SV.

Conclusions

In response to CPT, the high G tolerance group elevated MAP by increasing TPR, whereas the low G tolerance group showed a dependency on increased CO. The H group seemed to have a larger vasoconstrictor reserve. The results further suggest that vasoconstrictor reserve capacity could constitute the link between the recent finding that indicates a relationship between G tolerance and arterial distensibility in the legs.     

Effects of triglycyl-lysine-vasopressin on cardiovascular responses to orthostatic stress

The influence of triglycyl-lysine-vasopressin (TGLVP) on cardiovascular responses to orthostatic stress was studied. Arterial pressures, heart rate (HR) and stroke volume (SV) were measured in eight healthy males subjected to 20 min 70 degrees head-up tilt. On different days they received either 0.01 mg/kg b.w. of TGLVP or a corresponding volume of 0.9% saline i.v. after 15 min supine rest. After the drug injection, in supine subjects, HR had decreased from 58 to 50 beats min-1, total peripheral resistance (TPR) was elevated by 29%, systolic (SAP) and diastolic pressure (DAP) had increased by 7 and 8 mmHg, respectively. During tilt, values for HR and SAP were similar with and without TGLVP whereas DAP and MAP were elevated 8 and 7 mmHg, respectively, by the drug. 4-8 min into the tilt, TGLVP caused an 8% sustained curtailment of SV. Both with and without the drug TPR increased by about 30% in response to head-up tilt. Thus, the marked peripheral arteriolar constriction after vasopressin in the supine position was not affected by head-up tilt. Tilting also abolished the drug-induced elevation in SAP, most likely explained by the reduction in SV. Although TPR was markedly increased by TGLVP during head-up tilt, reflected in the behaviour of DAP, the response of SV speaks against any beneficial effect of this drug on orthostatic tolerance in healthy subjects.     

Comparison of a three‐quarter electrode band configuration with a full electrode band configuration for impedance cardiography

Impedance cardiography is a technique commonly used in psychophysiological studies. However, concerns about the utility of full circumferential band electrodes (FB) have been raised. The current study was designed to compare FB with a three‐quarter circumferential band configuration (PB). A total of 47 participants (66% female, mean [SD] age=20.4 [3.0] years) underwent 2 testing sessions, once using FB and once using PB. Session order was randomized and balanced. Each session consisted of 5 min of rest, math task, recovery, and cold pressor test. Average baseline and task pre‐ejection period (PEP), stroke volume (SV), cardiac output (CO), heart rate (HR), blood pressure (BP), and total peripheral resistance (TPR) was calculated from impedance cardiography and blood pressure monitoring. Participants were are asked to rate measures of comfort after each session. There were no significant difference between the mean levels of PEP, SV, CO, HR, and TPR for the PB versus the FB configurations. However, both systolic BP and diastolic BP were higher during the FB session. Intraclass correlations were high (r_icc=.63–.93) between PB and FB. Bland‐Altman analyses revealed a low level of bias (≤5%) between the configurations. Based on limits of agreement between ±30%, there was equivalence in PEP between the 2 configurations, and SV, CO, and TPR were close to reaching equivalence. Participants clearly indicated greater comfort with the PB configuration compared to the FB. The current study provides incremental evidence that suggests a three‐quarter PB configuration may be utilized for standard psychophysiological testing instead of the standard FB configuration. However, further studies are needed to validate the PB configuration against other techniques.     

Renal and hormonal responses to isotonic saline infusion after 3 days' head‐down tilt vs. supine and seated positions

Aim: The study aimed to determine whether prolonged exposure to simulated microgravity produces a level of thoracic volume receptor loading similar to that seen in the upright position or immediately after lying down. Methods: We used a cross‐over design to compare responses to a saline infusion in eight healthy subjects during a 4‐day, ?6° head‐down tilt (HDT) and in the acute seated and acute supine positions. Results: The first 24 h of HDT were associated with greater urinary excretion of water and sodium (UV, UNaV) than seated and acute supine [cumulative UV, 3035 ± 219, 2311 ± 156 (P < 0.05), and 2448 ± 182 mL (P < 0.05), respectively; cumulative UNaV, 256 ± 19, 180 ± 11 (P < 0.05), and 189 ± 15 mmol (P < 0.05), respectively]. Haemoglobin and haematocrit were increased after 24 h and plasma volume decreased after 48 h of HDT (P < 0.05). With prolongation of HDT, UV and UNaV returned near the baseline values, and plasma atrial natriuretic factor (ANF) and renin values returned to acute seated levels; in acute supine, ANF values were higher and renin lower than in the two other positions. After a 30‐min infusion of 20 mL kg^?1 isotonic saline on the fourth HDT day or during acute seated or acute supine, sodium excretion within 4 h was similar during HDT and acute seated (83 ± 6 and 84 ± 9 mmol, respectively) and greater during supine (104 ± 8 mmol, P < 0.05). The renin decrease was greater in HDT and seated than in supine. The plasma ANF increase was greater during HDT than during supine; during seated, plasma ANF was unchanged. Conclusion: These data suggest that, after 4 days of HDT, thoracic volume receptor loading returns to the same level as in the seated position, leading to blunted responses to volume expansion as compared with the acute supine position.     

Haemodynamic and ADH responses to central blood volume shifts in cardiac-denervated humans

Haemodynamic responses and antidiuretic hormone (ADH) were measured during body position changes designed to induce blood volume shifts in 10 cardiac transplant recipients to assess the contribution of cardiac and vascular volume receptors in the control of ADH secretion. Each subject underwent 15 min of a control period in the seated posture, then assumed a lying posture for 30 min at 6 degrees head-down tilt (HDT) followed by 30 min of seated recovery. Venous blood samples and cardiac dimensions (echocardiography) were taken at 0 and 15 min before HDT, 5, 15 and 30 min of HDT, and 5, 15 and 30 min of seated recovery. Blood samples were analysed for haematocrit, plasma osmolality, plasma renin activity (PRA) and ADH. Resting plasma volume (PV) was measured by Evans blue dye and per cent changes in PV during posture changes were calculated from changes in haematocrit. Heart rate (HR) and blood pressure (BP) were recorded every 2 min. In the cardiac transplant subjects, mean HR decreased (BP less than 0.05) from 102 b.p.m. pre-HDT to 94 b.p.m. during HDT and returned to 101 b.p.m. in seated recovery while BP was slightly elevated (P less than 0.05). PV was increased by 6.3% (P less than 0.05) by the end of 30 min of HDT but returned to pre-HDT levels following seated recovery. Plasma osmolality was not altered by posture changes. Mean left ventricular end-diastolic volume increased (P less than 0.05) from 90 +/- 5 ml pre-HDT to 105 +/- 4 ml during HDT and returned to 88 +/- 5 ml in seated recovery. Plasma ADH was reduced by 28% (P less than 0.05) by the end of HDT and returned to pre-HDT levels with seated recovery. PRA was also reduced by 28% (P less than 0.05) with HDT. These responses were similar to those of six normal cardiac-innervated control subjects and one heart-lung recipient. Therefore, cardiac volume receptors are not the only mechanism for the control of ADH release during acute blood volume shifts in man.     

Reproducibility of orthostatic changes in cerebral oxygenation in healthy subjects aged 70 years or older.

In the elderly, standing can frequently be accompanied by blood pressure (BP) changes and cerebral symptoms such as dizziness, fall, or even syncope, but this may vary from day-to-day. Therefore, we aimed to investigate the reproducibility of orthostatic responses of cerebral cortical oxygenation and systemic haemodynamics in elderly subjects. In 27 healthy elderly subjects (age 70-84 years), changes in systolic BP (SBP), diastolic BP (DBP), heart rate (HR) and stroke volume (SV) were continuously monitored by Finapres (Finger Arterial Pressure), and changes in oxyhaemoglobin ([O2Hb]) and deoxyhaemoglobin ([HHb]) concentrations were continuously measured over the right frontal cortex by near infrared spectroscopy (NIRS) during supine rest and 10 min of active standing on two separate occasions. SBP and DBP increased by 6.7 +/- 15.4 mmHg (P<0.05, mean +/- SD) and 8.2 +/- 6.4 mmHg (P<0.01), respectively, whereas HR increased by 9.5 +/- 5.0 bpm (P<0.01) and SV decreased by -8.3 +/- 7.4 ml (P<0.01) during standing on the first occasion. [O2Hb] decreased by -3.9 +/- 2.9 micromol l-1 (P<0.01), while [HHb] increased by 1.8 +/- 2.2 micromol l-1 (P<0.01). Group-averaged orthostatic changes in cortical oxygenation and systemic haemodynamics were very similar on the two occasions, although an intraindividual variation was found. Cortical oxygenation changes were not accompanied by severe cerebral symptoms. Active standing induced reproducible group-averaged frontal cortical oxygenation declines in healthy elderly subjects, although an intraindividual day-to-day variability was present, possibly related to the variability of orthostatic BP responses. These findings indicate that cerebral autoregulation fails to compensate completely for postural changes in elderly subjects, which might predispose elderly subjects to ischaemic cerebral symptoms.     

Stroke volume decreases during mild dynamic and static exercise in supine humans

Aim: The contributions of cardiac output (CO) and total peripheral resistance to changes in arterial blood pressure are debated and differ between dynamic and static exercise. We studied the role stroke volume (SV) has in mild supine exercise. Methods: We investigated 10 healthy, supine volunteers by continuous measurement of heart rate (HR), mean arterial blood pressure, SV (ultrasound Doppler) and femoral beat volume (ultrasound Doppler) during both dynamic mild leg exercise and static forearm exercise. This made it possible to study CO, femoral flow (FF) and both total and femoral peripheral resistance beat‐by‐beat. Results: During a countdown period immediately prior to exercise, HR and mean arterial pressure increased, while SV decreased. During mild supine exercise, SV decreased by 5–8%, and most of this was explained by increased mean arterial pressure. Dynamic leg exercise doubled femoral beat volume, while static hand grip decreased femoral beat volume by 18%. FF is tightly regulated according to metabolic demand during both dynamic leg exercise and static forearm exercise. Conclusion: Our three major findings are, firstly, that SV decreases during both dynamic and static mild supine exercise due to an increase in mean arterial pressure. Secondly, femoral beat volume decreases during static hand grip, but FF is unchanged due to the increase in HR. Finally, anticipatory responses to exercise are apparent prior to both dynamic and static exercise. SV changes contribute to CO changes and should be included in studies of central haemodynamics during exercise.     

Cardiovascular Function During Pre-Avoidance, Avoidance, and Post-Avoidance in Dogs

Four dugs, implanted with aortic blood flow probes and catheters, were trained to press a panel during signalled shock avoidance and switched to an hour of Sidman avoidance per day for a minimum of 10 days, Cardiovascular function (heart rate=HR; stroke volume=SV: blood pressure = BP; cardiac output = CO; total peripheral resistance =TPR; and maximum aortic (dp/dt) was determined during the hour preceding avoidance, during avoidance, and during a 10 min post-avoidance period, Data from 4 dogs were analyzed. Two behaviorally reactive dogs showed elevated BP due to increased TPR during pre-avoidance and increased CO during avoidance. Increases in SV. HR. and dp/dt, most pronounced at the beginning of avoidance, suggest a change in left ventricular function. Intercorrelations between HR and dp/dt revealed apparent influences of the Frank-Starting mechanism during pre-avoidance, and cardiac contractility during avoidance. The 2 remaining animals were less reactive and showed only some of the patterns consistently seen in the 2 more reactive dogs. The data were discussed in terms, of obtaining a model for early stages of human hypertension.     

Effects of unilateral jaw clenching on cerebral/systemic circulation and related autonomic nerve activity

Jaw clenching (clenching) is the result of an isometric contraction of jaw closing muscles. Because of the location of working muscles and afferent information during tooth contact, the effect of clenching on the cerebral and systemic circulation might differ from that of isometric limb exercise. This study aimed to investigate the characteristic changes in cerebral and systemic circulation during jaw clenching by comparing those during handgrip exercise. Subjects were 17 right-handed men. Bilateral middle cerebral arterial blood flow velocity (MCAV), electromyography (EMG) of contracting muscles, heart rate (HR) and blood pressure (BP) were measured during unilateral handgrip exercise and clenching tasks. Autonomic nerve activity was evaluated by analyzing fluctuations in HR and BP. MCAV was significantly increased during the task with significantly higher values on the non-working than working side irrespective of unilateral handgrip or unilateral jaw clenching. Changes in HR during jaw clenching were lower than those during handgrip exercise, and changes in vaso-motor sympathetic nerve activity during left jaw clenching were lower than those during left handgrip exercise. The present results indicate that, compared with handgrip exercise, unilateral jaw clenching promotes bilateral activation of MCAV with smaller effects on cardiac output and sympathetic nervous system activity.     

Changes in cerebral blood flow during and after 48 h of both isocapnic and poikilocapnic hypoxia in humans

During acclimatization to the hypoxia of altitude, the cerebral circulation is exposed to arterial hypoxia and hypocapnia, two stimuli with opposing influences on cerebral blood flow (CBF). In order to understand the resultant changes in CBF, this study examined the responses of CBF during a period of constant mild hypoxia both with and without concomitant regulation of arterial P(CO2). Nine subjects were each exposed to two protocols in a purpose-built chamber: (1) 48 h of isocapnic hypoxia (Protocol I), where end-tidal P(O2) (P(ET,O2)) was held at 60 Torr and end-tidal P(CO2) (P(ET,CO2)) at the subject's resting value prior to experimentation; and (2) 48 h of poikilocapnic hypoxia (Protocol P), where P(ET,O2) was held at 60 Torr and P(ET,CO2) was uncontrolled. Transcranial Doppler ultrasound was used to assess CBF. At 24 h intervals during and after the hypoxic exposure CBF was measured and the sensitivity of CBF to acute variations in P(O2) and P(CO2) was determined. During Protocol P, P(ET,CO2) decreased by 13% (P < 0.001) and CBF decreased by 6% (P < 0.05), whereas during Protocol I, P(ET,CO2) and CBF remained unchanged. The sensitivity of CBF to acute variations in P(O2) and P(CO2) increased by 103% (P < 0.001) and 28% (P < 0.01), respectively, over the 48 h period of hypoxia. These changes did not differ between protocols. In conclusion, CBF decreases during mild poikilocapnic hypoxia, indicating that there is a predominant effect on CBF of the associated arterial hypocapnia. This fall occurs despite increases in the sensitivity of CBF to acute variations in P(O2)/P(CO2) arising directly from the hypoxic exposure.     

Breast-feeding and maternal cardiovascular function

Two studies examined the effects of breast-feeding on maternal cardiovascular function. In the first experiment, groups of breast-feeding and bottle-feeding women were compared on preejection period (PEP), heart rate (HR), cardiac output (CO), and total peripheral resistance (TPR) recorded for 1-min periods before and during standard laboratory stressors. Compared with bottle-feeders, breast-feeders had higher CO throughout the session, and greater decreases in CO and increases in TPR during cold pressor. In the second experiment, HR and blood pressure (BP) were compared before and after one breast-feeding and one bottle-feeding session in a within-subjects design. Both feeding methods increased BP but decreased HR, and systolic BP was higher for the breast-feeding than the bottle-feeding condition. Both studies support the notion that breast-feeding alters maternal cardiovascular function, possibly through the actions of oxytocin.     

Influences on central hemodynamics in hemorrhage of beta 2-adrenergic vascular control mechanisms

Central hemodynamic responses evoked by standardized hemorrhage (exsanguination of 20 ml x kg bwt-1) were followed during 2 h in cats with intact and blocked vascular beta 2-adrenoceptors using the 'selective' beta 2-blocker, ICI 118, 551. In the first 10 min after bleeding blood pressure and cardiac output (CO) decreased and total peripheral resistance (TPR) increased by the same amount in the 'intact' and beta 2-blocked animals. Whereas blood pressure later on reached approximately the same hypotension level in both groups, other hemodynamic variables were distinctly different. In the 'intact' animals there was a gradual, partial recovery of stroke volume (SV) and CO in the face of a restoration to control of TPR. In the beta 2-blocked animals TPR continued to increase in the face of a maintained low CO and declining SV. The lower SV in the latter group was ascribed to abolition of beta 2-adrenergic restoration of plasma volume via absorption of tissue fluid into the circulation. The gradual decline of TPR in the 'intact' animals was attributed to beta 2-adrenergic dilator interaction with constrictor influences on the resistance vessels. It is concluded that beta-adrenergic vascular control mechanisms help to improve nutritional tissue blood flow during hemorrhage by increasing plasma volume, and hence venous return and CO, and by decreasing TPR. These reflex, beta 2-adrenergic circulatory events are similar to those aimed at in current shock therapy by transfusion and vasodilator treatment.     

Cardiovascular patterns associated with appetitive and defensive activation during affective picture viewing

In this study we assessed blood pressure (BP), heart rate (HR), stroke volume (SV), cardiac output (CO), and total peripheral resistance (TPR) in response to 13 picture series in 37 participants in order to investigate their hemodynamic response associated with activation of the appetitive and defensive motivational systems underlying emotional experience. BP and SV, but not TPR, increased with increasing self‐rated arousal, whereas HR decelerated more in response to negative than positive and neutral pictures. These findings suggest that modulation of the cardiovascular response to pictures is primarily myocardial. The observed response pattern is consistent with a configuration of cardiac sympathetic–parasympathetic coactivation. The relationships between self‐rated arousal, BP, and SV were mainly exhibited by men, suggesting that increases in the sympathetic inotropic effect to the heart with self‐rated arousal may be larger in men than in women.