Peripheral Circulatory Responses Research Articles

Effect of moderate-intensity treadmill exercise under different ambient temperatures on peripheral circulatory responses in young healthy adults

Exercise training has the potential for inducing enhancements in peripheral circulation, which can play important preventive and therapeutic roles in peripheral circulatory diseases. However, the relevant published studies show conflicting and inconclusive results. Furthermore, useful or optimum ambient temperature for this purpose has not yet been established. Therefore, we investigated the acute responses in peripheral circulation from exposure of healthy subjects to treadmill exercise under different ambient temperatures; A total of 12 young adult volunteers (males 6, females 6) randomly underwent three sessions of treadmill exercise for 30 min under three different ambient temperatures (10°C, 20°C, and 30°C), at a predetermined exercise intensity. Before and after the intervention, leg skin blood flow (SBF) was measured by laser Speckle flowgraphy and hand skin temperature (ST), by digital thermometry; After the cessation of treadmill exercise, compared to the corresponding baseline values, a significant increase in SBF was observed under all ambient temperature conditions (P<0.005). During intervention, ST showed a significant decrease at 10th min of intervention under all ambient temperatures (P<0.005) with a subsequent increasing trend in it. After intervention, a significant increase in ST was observed under 20°C condition only (P<0.05). Also, after intervention, the observed increase in systolic blood pressure was less significant under 20°C condition; Treadmill exercise appears to be a useful intervention modality in inducing improvements in peripheral circulation. However, exposure to treadmill exercise under or near 20°C ambient temperature might be recommended for the purpose.

Frailty is associated with impaired cerebral oxygenation recovery during

Abstract Frailty is associated with impaired peripheral circulatory responses to standing in older adults. However, little is known about how frailty affects cerebrovascular function during such activities of daily living. Here we investigate the association between frailty and cerebral oxygenation during standing in a large clinical cohort of fallers and fainters. Participants were recruited from a national Falls and Syncope unit and underwent an active stand test (5–10 minutes lying supine, 3 minutes standing) with concurrent monitoring of continuous blood pressure (BP) and heart rate (HR) and tissue saturation index (TSI) using near-infrared spectroscopy (NIRS). Frailty was measured using a count of deficits (27 morbidities). Robust linear regression was applied to study the association between features of dynamic cerebral oxygenation (changes from baseline at nadir, overshoot, 30s and steady state; and recovery rate) and frailty while correcting for covariates. A p-value <0.05 was considered significant. Frailty was associated with deficits in TSI at 30s after standing (β: −0.165, CI: (−0.261, −0.069), p=0.005), as well as a lower diastolic BP at 30s (β: −1.346, CI: (−2.287, −0.405), p=0.032) and standing steady-state (β: −1.182, CI: (−2.038, −0.325), p=0.032). When stratified by gender, frailty was associated in women with a lower TSI at overshoot (β: −0.174, CI: (−0.312, −0.037), p=0.043) and 30s (β: −0.216 (−0.344, −0.089), p=0.010), and impaired DBP recovery at overshoot (β: −1.623, CI: (−2.865, −0.391), p=0.045) and attenuated HR response at 30s (β: −0.701, CI: (−1.246, −0.155), p=0.036). No associations were found in men. Impaired cerebral oxygenation and BP responses to standing are associated with frailty in patients with falls and syncope, with stronger effects in women, suggesting that frailty may increase risk of hypoperfusion and consequent syncope, falls, and brain ageing. Our results demonstrate the clinical utility and feasibility of using NIRS in this context which can be used to further personalise patient management. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Irish Research Council Cerebral oxygenation and frailty

Do patients with syncope have a hyper-reactive autonomic nervous system?

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Irish Research Council (IRC): Government of Ireland Postgraduate Scholarship Programme 2018, Dublin, Ireland Fundació Universitària Agustí Pedro i Pons, Universitat de Barcelona, Barcelona, Spain. Background The origin of syncope, a transient loss of consciousness due to cerebral hypoperfusion, remains unclear. Recent studies suggest that a hypersensitive autonomic nervous system might be involved in the pathophysiology of vasovagal syncope (VVS). Purpose Here we test the hypothesis that patients with VVS have a hyper-reactive autonomic nervous system by investigating the peripheral haemodynamic responses during a standing (AS) test in a group of young VVS patients vs a control group. Methods A prospective sample of consecutive patients from a National Falls and Syncope Unit was recruited, and a convenience sample of young healthy community dwelling adults was recruited from a local university (16-30 years). Participants performed a 3 minute AS with continuous measurement of beat-to-beat blood pressure (BP), heart rate (HR), and cerebral oxygenation measured with near infrared spectroscopy. Baseline, steady-state and other time domain features were obtained for systolic BP (SBP) (i.e. nadir, overshoot, overshoot-to-nadir, overshoot-to-nadir recovery rate) and for HR (i.e. peak, trough, peak-to-trough, peak-to-trough recovery rate). Multiple linear regression was used to compare these features between patients and controls while correcting for covariates (p < 0.05 significant). Results Forty patients and 17 controls were included, the former group being younger ((20(5.5) vs 23(1) years, p = 0.003). During steady-state standing SBP was higher as compared to controls (β: 6.853, CI: (0.713 12.993), p = 0.029). Patient data trended toward lower steady-state HR (β: -5.262, CI:(-11.201 0.677), p = 0.081), together with a larger peak-to-trough difference (β: 7.212, CI:(1.329 -15.754), p = 0.096). Conclusion These results tend to support the hypothesis and previous literature suggesting the presence of autonomic hyper-reactivity in patients with syncope, presenting as an exaggerated peripheral circulatory response to standing. Understanding the pathophysiology of VVS can help us improve its assessment and develop better treatment pathways for these patients. Abstract Figure.

Peripheral Blood Flow Changes to Cutaneous and Muscular Beds in Response to Acute Hookah Smoking

Hookah (waterpipe) smoking is a growing tobacco epidemic. Though perceived as a safer tobacco alternative, hookah smoke contains, in addition to tobacco combustion products, large amounts of charcoal combustion products-implicated in cardiovascular disease-from the burning charcoal used to heat the flavored tobacco. To date, little is known on the vascular effects of hookah smoking. The aim of this study was to characterize the peripheral circulatory response to acute hookah smoking in cutaneous and muscular beds. In 21 healthy young adult habitual hookah smokers who did not smoke cigarettes (age 24 ± 1 years, mean ± SE), we measured plasma nicotine, exhaled carbon monoxide, skin blood flow (laser Doppler velocimetry) and calf muscle blood flow (strain-gauge plethysmography) before and for up to 60 minutes after ad lib hookah smoking. In nine subjects, nonsmoking time-control studies were performed. Hookah smoking, which increased plasma nicotine by 5.8 ng/ml (from 0.6 ± 0.1 to 6.4 ± 1.3, p <0.001) and exhaled carbon monoxide by 27 ppm (from 2.7 ± 0.2 to 29.5 ± 2.2, p <0.001), decreased skin blood flow by 23% (20.1 ± 2.8 to 14.8 ± 1.9 units, p <0.001) and increased skeletal muscle blood flow by 34% (2.3 ± 0.1 to 2.9 ± 0.2 units, p = 0.010). These responses required more than one hour to recover after smoking cessation. All cardiovascular parameters were unchanged in the nonsmoking time-control studies. Although perceived to be innocuous, hookah smoking produces acute cutaneous vasoconstriction with skeletal muscle vasodilation, a dissociated pattern of peripheral blood flow responses that is characteristic of nicotine and carbon monoxide. In conclusion, these findings provide objective evidence to challenge the perception that hookah smoking is a safer tobacco alternative.

A systematic review of studies investigating the effects of controlled whole-body vibration intervention on peripheral circulation.

The findings of the published studies investigating the changes in peripheral circulation induced by exposure to whole-body vibration (WBV) are not consensual or conclusive. Also, those studies did not consider the role of vibration magnitude on the peripheral circulatory responses making the interpretation of the observed findings difficult. We aimed to review the published literature investigating the effects of controlled WBV intervention on peripheral circulation by characterizing the relevant exposure conditions including vibration magnitudes, and ascertain the specific patterns of responses in peripheral circulation of the lower extremity from such exposure. A computerized search was performed in PubMed and Scopus using selected key search terms, and the relevant data were extracted. The vibration magnitude in the included studies frequently exceeded the limit specified in the International Standard ISO 2631-1 (1997) for such exposure. As observed, exposure to WBV with frequencies≤30Hz caused an improvement in peripheral blood flow (BF) and/or skin temperature (ST) of the lower extremity. In contrast, the responses in BF and ST from exposure to WBV of higher frequencies (31Hz-50Hz) produced conflicting results. The findings of this review indicate that WBV exposure with relatively lower frequency and magnitude can be safely and effectively used to induce improvements in peripheral circulation. For this purpose, the limits recommended by the ISO 2631-1 (1997) should be considered till safe and effective vibration-related parameters are established.

Brachial and middle cerebral artery blood flow responses during sinusoidal leg cycling exercise

To examine the control of peripheral circulation to non‐active muscle and brain during leg cycling exercise, we measured the dynamics of brachial artery (BA) and middle cerebral artery (MCA) blood flow (BF) to sinusoidal (sine) work rate (WR) forcing. Nine healthy subjects performed upright leg cycle exercise with a constant WR for 30 min followed by 16‐min sine WR exercises of 4‐min period fluctuated between 20 W to 60% VO2max. During protocol, we measured pulmonary gas exchange [breath‐by‐breath], heart rate (HR) and mean arterial blood pressure (MAP) [Photoplethysmograph], blood velocity (BV) and cross sectional area of BA [Ultrasound Pulsed‐Doppler], BV of MCA [Transcranial Doppler Ultrasonograph], and forearm and forehead skin BF (SBF) [Laser Doppler] and sweating rate (SR) [Capacitance Hygrometry]. The variable was fitted as y(t)=M+A*sin((2π/T)*t‐θ), where t: time, A/M: relative amplitude, T: period, θ: phase shift. Almost variables traced the sine wave adequately. The phase of variables regarding O2‐transport such as VO2, HR followed sine WR with similar delays (the mean: VO2; 51, HR; 45 °). While the BV in MCA showed the similar phase (73 °), its A/M was small (4.5 %). Contrarily, the response of BA displayed an anti‐phase (175 °) and a large A/M (30 %). The peripheral circulatory responses to nonactive limb and brain is quite different. (Support: JSPS‐KAKENHI, 22370091, 23650390, 24700701, 24247046)

Frequency spectrum analysis of finger photoplethysmographic waveform variability during haemodialysis

This study investigates the peripheral circulatory and autonomic response to volume withdrawal in haemodialysis based on spectral analysis of photoplethysmographic waveform variability (PPGV). Frequency spectrum analysis was performed on the baseline and pulse amplitude variabilities of the finger infrared photoplethysmographic (PPG) waveform and on heart rate variability extracted from the ECG signal collected from 18 kidney failure patients undergoing haemodialysis. Spectral powers were calculated from the low frequency (LF, 0.04–0.145 Hz) and high frequency (HF, 0.145–0.45 Hz) bands. In eight stable fluid overloaded patients (fluid removal of >2 L) not on alpha blockers, progressive reduction in relative blood volume during haemodialysis resulted in significant increase in LF and HF powers of PPG baseline and amplitude variability (P < 0.01), when expressed in mean-scaled units. The augmentation of LF powers in PPGV during haemodialysis may indicate the recovery and possibly further enhancement of peripheral sympathetic vascular modulation subsequent to volume unloading, whilst the increase in respiratory HF power in PPGV is most likely a sign of preload reduction. Spectral analysis of finger PPGV may provide valuable information on the autonomic vascular response to blood volume reduction in haemodialysis, and can be potentially utilized as a non-invasive tool for assessing peripheral circulatory control during routine dialysis procedure.

NIRS application in evaluating threaded-fastener driving assembly tasks

Repetitive use of hand-held power tools, due to their potential to generate forces greater than an operator capacity, is associated with work-related upper extremity musculoskeletal disorders. This laboratory study investigated the effects of power tool-induced torque reaction and work:rest pattern on peripheral circulatory responses during repetitive nutrunner operations. Twenty men completed eight fastener-driving sessions that consisted of two different work:rest patterns of 360 repetitive tasks both at slow- and fast-pace using a pneumatic nutrunner, which was equipped with an instrumented tool handle with a custom-designed force gauge that measures grip force in real time, on a torque reaction assembly joint and a control joint. Near-infrared spectroscopy (NIRS) was simultaneously used to monitor changes in tissue oxygenation and blood volume from flexor digitorum superficialis and extensor digitorum communis. The mean grip force exerted by participants during sessions with no torque buildup was 33% of their maximum voluntary contraction whereas during sessions with torque buildup it was of 57% maximum voluntary contraction. Additionally, throughout a session the rate of changes in grip force decreased more with the latter (−0.007 and −0.022 N/drive, respectively) suggesting considerable effort during torque buildup by the participants. Correspondingly, in the flexor muscles greater deoxygenation was observed than that of extensor muscles for all sessions, suggesting greatest metabolic demand from the flexors during torque buildup. Tissue oxygenation index, representing the dynamic balance between oxygen delivery and oxygen consumption in the tissue was similar during both combinations of pace and work:rest ratios in the flexors. On the contrary, tissue oxygenation index in the extensor region was higher during sessions of slow-pace and work with rest breaks compared to sessions of fast-pace and work with no rest, suggesting that the tool operations with faster work pace and continuous work with no rest breaks results in greatest decrease in oxygen saturation. These findings imply that spectroscopy-derived measures are able to reflect upper extremity physical demands experienced by the tool operators, and therefore NIRS is a useful alternative technique to broaden the understanding of tissue physiological changes resulted from upper extremity activities. Relevance to the industry With advances in technology, more hand-held power tools are repetitively being used on assembly lines in various industries. Although powered tools enhance performance and efficiency, these tools have the potential to result in forces that are often associated with development of musculoskeletal disorders in the upper extremities. This study provided an alternative, non-invasive physiological approach to enhance the understanding of man (hand) and machine (tool) interaction in work productivity factors (e.g., work pace and work:rest patterns).

Peripheral circulatory responses in vivo from regional brachial biceps and lumbar muscles in healthy men and women during pushing and pulling exercise

Although women have been performing increasingly more manual labor in the workplace in the past 2 decades, their physiological responses and gender-based differences in muscle microvascularity during occupational activities have not yet been extensively documented. This study assessed gender differences and tissue heterogeneity in peripheral circulatory responses from 2 muscle groups during pushing and pulling exercise until volitional exhaustion. In healthy men and women, near-infrared spectroscopy was used to determine peripheral responses, oxygenation, and blood volume simultaneously from the right biceps brachii and lumbar erector spinae. Pulmonary oxygen uptake was assessed using a metabolic measurement cart. Although the 11 men who participated in the study demonstrated greater pulmonary oxygen uptake and power output at volitional exhaustion, their peak peripheral responses for both muscles were similar to those of the 11 women participating. In both sexes, oxygenations trends decreased in both muscles with an increase in workload. However, whereas blood volume increased in the biceps, it decreased in the lumbar muscle in both sexes. At 20% to 60% levels of peak pulmonary oxygen uptake, the percent change in peripheral bicep responses was greater for men than for women (P < 0.05). In contrast, women demonstrated greater change in lumbar muscle oxygenation compared with men at 40% to 60% of peak pulmonary oxygen uptake (P < 0.05). Similar peripheral responses for biceps and lumbar muscles at the point of volitional exhaustion suggest that gender differences in pulmonary oxygen uptake are independent of oxygen extraction or delivery across the muscle groups monitored. However, at submaximal levels of exercise, the peripheral changes in each muscle were gender dependent. Although biceps and lumbar muscles are 2 discrete muscle groups, based on the heterogeneity found in the blood volume trends it is likely that oxygen supply and demand are regulated by muscle location and muscle fiber characteristics. Overall, gender-based assessment of occupational activities should incorporate both pulmonary and peripheral circulatory responses to understand each sex's performance effectiveness.

E105 手腕振動曝露が及ぼす末梢循環反応におけるハンドル表面温度影響の検討(振動障害,一般演題:口演,地方の時代の産業保健,第79回日本産業衛生学会)

E105 手腕振動曝露が及ぼす末梢循環反応におけるハンドル表面温度影響の検討(振動障害,一般演題:口演,地方の時代の産業保健,第79回日本産業衛生学会)

Fetal cerebral and peripheral circulatory responses to hypoxia after nitric oxide synthase inhibition.

The increase in cerebral blood flow (CBF) during hypoxia in fetal sheep at 0.6 gestation is less than the increase at 0.9 gestation when normalized for differences in baseline CBF and oxygen consumption. Nitric oxide (NO) synthase (NOS) catalytic activity increases threefold during this period of development. We tested the hypothesis that administration of the NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) decreases the CBF response to systemic hypoxia selectively at 0.9 gestation. We also tested whether any peripheral vasoconstriction during hypoxia is potentiated by L-NAME at 0.9 gestation. Administration of L-NAME increased arterial blood pressure and decreased microsphere-determined CBF during normoxia in fetal sheep at both 0.6 and 0.9 gestation. With subsequent reduction of arterial oxygen content by approximately 50%, the percent increase in forebrain CBF in a control group (57 +/- 11%; +/- SE) and L-NAME-treated group (51 +/- 6%) was similar at 0.6 gestation. Likewise, at 0.9 gestation, the increase in CBF was similar in control (90 +/- 25%) and L-NAME (80 +/- 28%) groups. At 0.9 gestation, L-NAME treatment attenuated the increase in coronary blood flow and increased gastrointestinal vascular resistance during hypoxia. We conclude that NO exerts a basal vasodilatory influence in brain as early as 0.6 gestation in fetal sheep but is not an important mechanism for hypoxic vasodilation in brain at either 0.6 or 0.9 gestation. Thus the developmental increase in NOS catalytic capacity does not appear to be responsible for developmental increases in the CBF response to hypoxia during this period. In contrast, NO modulates the vascular response to hypoxia in heart and gastrointestinal tract.

Periodic, Profound Peripheral Vasoconstriction—A New Marker of Obstructive Sleep Apnea

We report a novel approach to the determination of sleep apnea based on measuring the peripheral circulatory responses in a primary condition of disordered breathing. The apparatus is a finger plethysmograph coupled to a constant volume, variable pressure, pneumatic system. The plethysmograph's tip (measurement site) is composed of two parallel opposing longitudinal half thimbles, which is attached to a contiguous annular cuff. Each compartment consists of an internal membrane surrounded by an outer rigid wall. These provide a uniform pressure field and impart a two-point locking action preventing axial and longitudinal motion of the finger. Subdiastolic pressure is applied to prevent venous pooling, engorgement, and stasis, to inhibit retrograde venous shock wave propagation and partially unload arterial wall tension. The annular cuff extends the effective boundary of the pressure field beyond the measuring site. In 42 patients with Obstructive Sleep Apnea Syndrome (OSAS) profound, transient vasoconstriction and tachycardia usually of a periodic nature, were clearly seen with each apneic event, possibly related to transient arousal. Good agreement was found between standard total apnea-hypopnea scoring, 129.5+/-22.4 (Mean +/- SEM), and transient vasoconstriction and tachycardia events, 121.2+/-19.4 (R = .92, p<.0001). We conclude that the finger tip exemplifies the scope of peripheral vascular responsiveness due to its high density of alpha sympathetic innervation, and its high degree of blood flow rate lability. Given that elevated peripheral resistance and tightly linked transient heart rate elevation is a consistent part of the hemodynamic response to arousal and OSAS, we believe that pulsatile finger blood flow patterns can be clearly diagnostic of OSAS and other sleep-disordered breathing conditions.

Effects of scorpion venom on central and peripheral circulatory response in an open-chest dog model.

Scorpion venom can induce in dogs severe haemodynamic changes leading to rapid rise in systemic blood pressure and cardiac output, followed by reduction of cardiac output and blood pressure within 1 h. The decrease in cardiac output is not related to myocardial dysfunction (Tarasiuk et al. 1994). We hypothesized that scorpion venom affects cardiac output by reducing venous return to the heart. Venous return was studied by steady-state measurements of cardiac output, the pressure gradient and resistance to venous return, in 16 dogs following injection of 0.05 mg kg-1 venom obtained from the scorpion species Leiurus quinquestriatus. In eight of the 16 dogs, atropine (0.1 mg kg-1) was given 15 min prior to venom injection (n = 4) or 85 min (n = 4) after venom administration. In five additional dogs, the stability of the preparation over time was evaluated following the same protocol without the injection of the venom. At 15 min, the venom induced an increase in blood pressure (80%) and cardiac output (250%) (P < 0.001) with little effect on heart rate. At 90 min, cardiac output and heart rate declined considerably below baseline (P < 0.001). Atropine prevented the decrease in heart rate, but did not affect the reduction of cardiac output. Five minutes after venom injection, mean circulatory pressure increased by 300% (P < 0.001), which was accompanied by a rightward shift of the venous return curve with no effect on resistance to venous return. At 120 min, mean circulatory pressure recovered and resistance to venous return remained at 40% (P < 0.01) above baseline. This study indicates that, in dogs, scorpion venom affects cardiac output by modifying the determinants of venous return. The initial increase in cardiac output is related to increased mean circulatory pressure since resistance to venous return did not change. The later fall in cardiac output is related to the reduction of mean circulatory pressure and increased resistance to venous return.

Peak skeletal muscle perfusion is maintained in patients with chronic heart failure when only a small muscle mass is exercised.

The issue to be resolved was whether peripheral leg blood flow in patients with chronic heart failure (CHF) is reduced by low local flow capacity or as a function of the amount of muscle mass activated during exercise. In ten CHF patients (ejection fraction 26 (9)%), and 12 healthy controls central and peripheral circulatory responses were assessed during dynamic one- and two-legged knee extensor work. The patients reached a peak perfusion of 234 (16) ml 100 g-1 min-1 in the one-legged mode, which was similar to the controls (244 (11) ml 100 g-1 min-1). At peak two-legged work muscle perfusion was reduced in the patients by 24% (P < 0.05). In contrast the controls maintained their peak muscle perfusion. The mass of the quadriceps femoris muscle and peak leg blood flow correlated closely for both groups at peak one-legged work (r = 0.85, P < 0.001). Peak oxygen uptake in the active limb during one-legged exercise was similar for patients and controls (0.52 (0.06) vs. 0.63 (0.06) l min-1), but it was 38% lower (P < 0.05) in patients than controls during exhaustive two-legged exercise. Arterial systemic oxygen delivery (cardiac output x arterial oxygen content), at peak exercise was highly correlated with peak one- and two-legged workload for both groups, explaining 70% of the difference in peak workload attained (P < 0.001). At peak two-legged exercise non-exercising tissues of the body in the male CHF patients with the largest limb muscle mass, received a blood flow of only 1.2 (0.7) 1 min-1. Mean arterial blood pressure at peak work in both test conditions was significantly lower for the patients than the controls. A higher sympathetic nerve activity in the patients, as evaluated by arterial noradrenaline concentration (NA) and leg NA spillover, contributed to maintain the perfusion pressure. Patients with moderate CHF can reach a peak skeletal muscle perfusion and a leg oxygen uptake comparable to that of healthy individuals when a sufficiently small muscle mass is activated. Exercise involving a larger muscle mass, for the patients in this study about 4 kg, markedly reduces peak leg blood flow, perfusion and oxygen uptake as well as blood flow to non-exercising organs and tissues.

Peripheral Circulatory Response in Cardiac Failure

Derangements of the peripheral circulation play a major role in the pathophysiology of congestive heart failure. Their appearance coincides with that of the symptoms and signs that characterize the full-blown clinical syndrome. Long-term therapy with ACE inhibitors partially reverses these abnormalities, but the pathologic mechanisms are still poorly understood.

Cardiocirculatory Responses to AII and AVP in Conscious Rats

Cardiac and peripheral circulatory responses to changes in afterload with angiotensin II (AII) and vasopressin (AVP) were investigated in ganglion-blocked (hexamethonium) conscious rats. Cardiac output (CO) was measured by thermodilution. Both hormones were infused at a dose adjusted to increase mean arterial pressure 70% above baseline. AVP (11.4 +/- 2.2 ng/kg/min, n = 6) decreased CO from 43.4 +/- 2.3 to 34.1 +/- 2.9 ml/min/100 g (p less than 0.001), whereas AII (33.4 +/- 7.4 ng/kg/min, n = 7) increased CO from 38.7 +/- 2.6 to 44.9 +/- 3.4 ml/min/100 g (p less than 0.01). Heart rate did not change with the increase in afterload with either vasoconstrictor. To study whether the different effects of AII and AVP on CO may be explained by their different actions on the venous system, changes in venous tone were evaluated by measuring mean circulatory filling pressure (MCFP) and determining the pressure gradient for venous return (PGVR). AVP changed neither MCFP nor PGVR, whereas AII increased both these parameters, 20.7 +/- 2.8% (p less than 0.01) and 20.3 +/- 6.4% (p less than 0.01), respectively, above control. We also examined the effects of AII and AVP on ventricular dynamics: left ventricular systolic pressure and left ventricular dP/dtmax increased as aortic pressure was increased in a similar manner with both vasoconstrictors. However, AVP induced a greater increase in left ventricular end diastolic pressure than AII. Our results indicate that AII induces an increase in preload by its effect on venous tone, which is adequate to increase cardiac output. The decrease in cardiac output induced by increasing afterload with AVP can be explained by two mechanisms: an inadequate venous return and a failure of the left ventricle to overcome the increased afterload.

Peripheral circulatory responses to sustained handgrip in workers using vibrating tools.

In order to study the effects of static force such as a handgrip in detail, the peripheral circulatory function and the autonomic nervous function of workers who used chain-saws were examined in a handgrip test at 30% of maximum voluntary contraction (30% MVC). Workers using chain-saws were divided into three groups: group A without any symptoms, group B with numbness and/or pain but without Raynaud's phenomenon and group C with Raynaud's phenomenon. The results obtained were as follows: 1. The finger blood flow (FBF) of all groups significantly decreased during the handgrip and significantly increased after the end of the handgrip as compared with the initial value. There was a tendency for the FBF decrease of group C to be less than that of group A. 2. The mean value of both maximum FBF decrease and maximum FBF increase during handgrip tests fell in alphabetical order (A, B, C). The maximum FBF increase of group C was significantly less than that of group A. 3. The finger skin temperature (FST) of each group significantly fell during the handgrip but there was no significant difference among the three groups. FST returned to the level of the initial value one minute after the end of the handgrip, and significantly rose two minutes and three minutes after the end of the handgrip as compared with the initial value. 4. Both the systolic blood pressure and the diastolic blood pressure of all groups significantly rose during the handgrip but there was no significant difference among the three groups. Concerning the maximum rise of diastolic blood pressure, which is an indicator of autonomic nervous function, there was no significant difference among the three groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral and peripheral circulatory responses to intracranial hypertension in fetal sheep.

Fetal head compression during normal labor can increase intracranial pressure (ICP). We studied the cerebral and peripheral blood flow responses to ICP elevation in utero in chronically catheterized fetal sheep using the radiolabeled microsphere technique. ICP was elevated, stepwise, in increments of 6 +/- 1 mm Hg by infusion of artificial cerebrospinal fluid into a lateral ventricle. When ICP was raised to within 28 mm Hg of baseline mean arterial blood pressure (i.e., ICP above 22 mm Hg), arterial pressure began to increase. Above this ICP level, up to 41 mm Hg, mean cerebral perfusion pressure was maintained by equivalent increases in arterial pressure. Cerebral blood flow and O2 uptake at the highest ICP levels were not different from baseline values. Changes in peripheral organ blood flow were graded according to the level of ICP. At the highest level (ICP = 41 mm Hg), renal, gastrointestinal, and skin blood flow decreased by 68%, 69%, and 65%, respectively. Myocardial and adrenal blood flow doubled, whereas heart rate and cardiac output were unchanged. Placental blood flow increased in proportion to arterial pressure. Arterial plasma epinephrine, norepinephrine and arginine vasopressin increased by nearly two orders of magnitude. Therefore, as ICP approaches baseline mean arterial pressure, fetal lambs are capable of sustaining cerebral perfusion by initiating profound visceral vasoconstriction without curtailing placental blood flow. Since cerebral O2 uptake was maintained, there is no evidence that stimulation of the peripheral response requires pronounced cerebral ischemia. This highly developed Cushing response may be important for ensuring cerebral viability when the fetal head is compressed during parturition.

Cardiac and peripheral circulatory responses to angiotension and vasopressin in dogs.

To determine the cardiac and peripheral circulatory responses to changes in afterload with angiotension and vasopressin, we increased mean aortic pressure 25% and 50% above control in splenectomized and ganglion-blocked dogs. We compared these responses to similar mechanical increases in aortic pressure produced by partial balloon occlusion of the descending aorta. With 25% or 50% increases in aortic pressure, angiotensin, vasopressin, and balloon inflation produced no changes in heart rate, right atrial, and mean pulmonary artery pressures. At 25% increase in aortic pressure, cardiac output was maintained with angiotensin and balloon occlusion but decreased with vasopressin. At 50% increase in aortic pressure, cardiac output was maintained with only balloon occlusion and decreased with both angiotensin and vasopressin. Whenever cardiac output fell, central blood volume did not increase as after-load increased. These changes in preload can be explained by alterations in the venous circulation. Vasopressin did not alter venous compliance or unstressed vascular volume but increased resistance to venous return. Angiotensin also increased resistance to venous return but decreased venous compliance and did not change unstressed vascular volume. Balloon occlusion had no effects on these parameters. We conclude that: (a) angiotensin caused significant venoconstriction resulting in maintenance of cardiac output at 25% but not 50% increase in aortic pressure; (b) vasopressin increased the resistance to venous return without venoconstriction; this resulted in a fall in cardiac output even with a 25% increase in aortic pressure; and (c) the effects of the agents on the venous circulation were independent of the mechanical effects of a pressure increase in the arterial circulation.

Effects of acute hypoxia and CO2 inhalation on systemic and peripheral oxygen uptake and circulatory responses during moderate exercise.

The effect of acute hypoxia and CO2 inhalation on leg blood flow (LBF), on leg vascular resistance (LVR) and on oxygen supply to and oxygen consumption in the exercising leg was studied in nine healthy male subjects during moderate one-leg exercise. Each subject exercised for 20 min on a cycle ergometer in four different conditions: normoxia, normoxia + 2% CO2, hypoxia corresponding to an altitude of 4000 m above sea level, and hypoxia + 1.2% CO2. Gas exchange, heart rate (HR), arterial blood pressure, and LBF were measured, and arterial and venous blood samples were analysed for PCO2, PO2, oxygen saturation, haematocrit and haemoglobin concentration. Systemic oxygen consumption was 1.83 l.min-1 (1.48-2.59) and was not affected by hypoxia or CO2 inhalation in hypoxia. HR was unaffected by CO2, but increased from 136 beat.min-1 (111-141) in normoxia to 155 (139-169) in hypoxia. LBF was 6.5 l.min-1 (5.4-7.6) in normoxia and increased significantly in hypoxia to 8.4 (5.9-10.1). LVR decreased significantly from 2.23 kPa.l-1.min (1.89-2.99) in normoxia to 1.89 (1.53-2.52) in hypoxia. The increase in LBF from normoxia to hypoxia correlated significantly with the decrease in LVR. When CO2 was added in hypoxia a significant correlation was also found between the decrease in LBF and the increase in LVR. In normoxia, the addition of CO2 caused a significant increase in mean blood pressure. Oxygen consumption in the exercising leg (leg VO2) in normoxia was 0.97 l.min-1 (0.72-1.10), and was unaffected by hypoxia and CO2.(ABSTRACT TRUNCATED AT 250 WORDS)