Finger Cuff Research Articles

Analysis of cardiovascular oscillations: A new approach to the early prediction of pre-eclampsia

Pre-eclampsia (PE) is a serious disorder with high morbidity and mortality occurring during pregnancy; 3%-5% of all pregnant women are affected. Early prediction is still insufficient in clinical practice. Although most pre-eclamptic patients show pathological uterine perfusion in the second trimester, this parameter has a positive predictive accuracy of only 30%, which makes it unsuitable for early, reliable prediction. The study is based on the hypothesis that alterations in cardiovascular regulatory behavior can be used to predict PE. Ninety-six pregnant women in whom Doppler investigation detected perfusion disorders of the uterine arteries were included in the study. Twenty-four of these pregnant women developed PE after the 30th week of gestation. During pregnancy, additional several noninvasive continuous blood pressure recordings were made over 30 min under resting conditions by means of a finger cuff. The time series extracted of systolic as well as diastolic beat-to-beat pressures and the heart rate were studied by variability and coupling analysis to find predictive factors preceding genesis of the disease. In the period between the 18th and 26th weeks of pregnancy, three special variability and baroreflex parameters were able to predict PE several weeks before clinical manifestation. Discriminant function analysis of these parameters was able to predict PE with a sensitivity and specificity of 87.5% and a positive predictive value of 70%. The combined clinical assessment of uterine perfusion and cardiovascular variability demonstrates the best current prediction several weeks before clinical manifestation of PE.

Legcycling Improves the Oxygenation in Relaxed Shoulder Muscles

Physical activity can reduce the risk for e.g. cardiovascular diseases, however only relatively few studies have considered the effect of physical activity upon muscle pain e.g. in trapezius myalgia. Training of the painful muscles itself may have a positive effect but compliance may be low for such intervention due to pain being provoked. We therefore hypothesized that training of other large muscle groups may have an effect even upon the oxygenation of the passive muscles mediated by the systemic cardiovascular response to exercise. Thus even though the painful shoulder muscles are not directly trained they could benefit from an increased oxygen availability due to leg exercise PURPOSE: To determine the oxygenation in the passive upper trapezius muscles during leg cycling together with systemic blood pressure. METHODS: Five healthy female subjects and 13 female patients diagnosed with trapezius myalgia in one or both shoulder. The most painful shoulder (P) was compared to the dominant side of the healthy subjects (D). The subjects performed 20 min sub maximal cycle ergometer exercise with their arms hanging relaxed along the side. The exercise started at a level of 55% of maximal heart rate for 10 min. and was increased to 70% for the last 10 min. The exercise was followed by a 5 min. recovery period. Muscle tissue oxygenation was measured using Near Infrared Spectroscopy, NIRS (NIRO 300 Hamamatsu, Japan). The NIRS probes were placed bilaterally on the upper trapezius muscles. Blood pressure was measured continuously with a finger cuff on the right hand (Finometer, Finland). Five measurements of 30 s. were analysed: in the beginning (after 11/2 min.), 1. steady state, 2.steady state, in the end of the work period (19 min.) and 2 min. after the exercise (recovery). RESULTS: For all subjects an increase in oxygenation was found for both shoulders from start to end (P/D: 0,4±1 – 6±3; NoP/NonD: −0,7±1 – 5±3μM) with an even larger increase in the recovery period. (P/D: 8±4; NoP/NonD: 8±3μM). No increase in BP was found neither in systolic nor diastolic pressure but a tendency to a small decrease was present (179/65±23/13 – 165/61±31/11 mmHg).When the painful shoulder of the patients with diagnosed trapezius myalgi were compared to healthy subjects a significantly higher oxygenation was present in the end of the working period and in the recovery period for the healthy subjects. CONCLUSION: Exercise with large muscle groups has an effect upon small muscles at rest regarding oxygenation, this effect is larger in non myalgic shoulders.

A combined technique for predicting pre-eclampsia: concurrent measurement of uterine perfusion and analysis of heart rate and blood pressure variability

Pre-eclampsia is a serious complication of pregnancy with high morbidity and mortality and an incidence of 3-5% in all pregnancies. Early prediction is still insufficient in clinical practice. Although most pre-eclamptic patients have pathological uterine perfusion in the second trimester, perfusion disturbance has a positive predictive accuracy (PPA) only of approximately 30%. Non-invasive continuous blood pressure recordings were taken simultaneously via a finger cuff for 30 min. Time series of systolic as well as diastolic beat-to-beat pressure values were extracted to analyse heart rate and blood pressure variability and baroreflex sensitivity in 102 second-trimester pregnancies, to assess predictability for pre-eclampsia (n = 16). All women underwent Doppler investigations of the uterine arteries. We identified a combination of three variability and baroreflex parameters to best predict pre-eclampsia several weeks before clinical manifestation. The discriminant function of these three parameters classified patients with later pre-eclampsia with a sensitivity of 87.5%, a specificity of 83.7%, and a PPA of 50.0%. Combined with Doppler investigations of uterine arteries, PPA increased to 71.4%. This technique of incorporating one-stop clinical assessment of uterine perfusion and variability parameters in the second trimester produces the most effective prediction of pre-eclampsia to date.

Principles and techniques of blood pressure measurement

The gold standard for clinical blood pressure measurement continues to be readings taken by a physician using a mercury sphygmomanometer, but this is changing as mercury is gradually being phased out. The oscillometric technique, which primarily detects mean arterial pressure, is increasingly popular for use in electronic devices. Other methods include ultrasound (used mainly to detect systolic pressure) and the finger cuff method of Penaz, which can record beat-to-beat pressure noninvasively from the finger. The preferred location of measurement is the upper arm, but errors may occur because of changes in the position of the arm. Other technical sources of error include inappropriate cuff size and too rapid deflation of the cuff. Clinic readings may be unrepresentative of the patient's true blood pressure because of the white coat effect, which is defined as the difference between the clinic readings and the average daytime blood pressure. Patients with elevated clinic pressure and normal daytime pressure are said to have white coat hypertension. There are three commonly used methods for measuring blood pressure for clinical purposes: clinic readings, self-monitoring by the patient at home, and 24-hour ambulatory readings. Self-monitoring is growing rapidly in popularity and is generally carried out using electronic devices that work on the oscillometric technique. Although standard validation protocols exist, many devices on the market have not been tested for accuracy. Such devices can record blood pressure from the upper arm, wrist, or finger, but the arm is preferred. Twenty-four-hour ambulatory monitoring has been found to be the best predictor of cardiovascular risk in the individual patient and is the only technique that can describe the diurnal rhythm of blood pressure accurately. Ambulatory monitoring is mainly used for diagnosing hypertension, whereas self-monitoring is used for following the response to treatment. Different techniques of blood pressure measurement may be preferred in certain situations. In infants the ultrasound technique is best, whereas in pregnancy and after exercise the diastolic pressure may be hard to measure using the conventional auscultatory method. In obese subjects it is important to use a cuff of the correct size.

Cerebral autoregulation among patients with symptoms of hydrocephalus.

To study the relationship between the resistance to cerebrospinal fluid (CSF) outflow and cerebral autoregulation. We examined 35 patients who presented with ventricular dilation and clinical symptoms of communicating hydrocephalus. For all of these patients, CSF compensatory reserve was investigated by using a computerized infusion test, with simultaneous recording of blood flow velocity wave forms (by using transcranial Doppler ultrasonography) and arterial blood pressure (with a Finapress finger cuff). The resistance to CSF outflow was calculated as the absolute increase in intracranial pressure (interpolated over vasogenic waves) divided by the infusion rate (1.5 ml/min in most cases). The index of autoregulation was assessed as a correlation coefficient (moving time window of 5 min) between slow waves (with periods of 20 s to 2 min) in mean blood flow velocity and cerebral perfusion pressure. The mean intracranial pressure increased during the test, from 6 mm Hg (standard deviation, 6 mm Hg) to 20 mm Hg (standard deviation, 10 mm Hg) (P < 0.0001). The index of autoregulation was significantly correlated with the resistance to CSF outflow (r = -0.41, P < 0.03), indicating better autoregulation with greater resistance to CSF outflow. Patients presenting with ventricular dilation may exhibit either decreased (atrophy) or increased (normal-pressure hydrocephalus) resistance to CSF outflow. Increased resistance is correlated with preserved autoregulation. Patients with low resistance, suggesting brain atrophy, more often have disturbed autoregulation in the middle cerebral artery territory, as assessed by transcranial Doppler ultrasonography.

Acute cardiovascular responses to leg-press resistance exercise in heart transplant recipients

Background: Reduced skeletal muscle strength is characteristic of individuals following heart transplantation. Weight lifting exercise has been demonstrated as an effective means by which to increase muscular strength in other cardiac patients but the appropriateness of this form of exercise in heart transplant patients has not been investigated. The purpose of this study was to describe the cardiovascular responses of heart transplant patients to a single, prolonged bout of weight lifting training. Methods: Twenty-three heart transplant recipients were stratified into early (Early; 3 months; n=6), intermediate (Intermediate; 1–3 years; n=7) and late (Late; 5–14 years; n=10) post transplant groups and studied in four experimental conditions: supine rest, upright rest, single leg-press exercise (28 repetitions over 2 min 20 s at 50% 1 repetition maximum) and recovery. Swan-Ganz catheterization allowed measurement of right heart pressures and cardiac output by thermodilution. Systemic arterial pressures and heart rate were measured continuously using a non-invasive finger cuff. Results: Cardiac output increased by 30, 40 and 54% during exercise in Early, Intermediate and Late, respectively. Heart rate increased by 4.5% in Early compared to 11 and 16% increases in Intermediate and Late. At peak exercise, systolic blood pressures reached average values of 179±9, 180±14 and 176±8 mmHg in Early, Intermediate and Late, respectively. Average mean pulmonary artery pressure did not exceed 30 mmHg and average pulmonary wedge pressure did not exceed 15 mmHg in any group during the exercise. Conclusions: These observations indicate that a lengthened set of single leg-press exercise at a moderate lifting intensity can be performed within safe and acceptable physiological limits in patients following heart transplantation. To better address the specific rehabilitation needs of heart transplant recipients, future research should focus on developing training programs which include weight lifting exercise.

Development of a Finger Cuff Unit for a Noninvasive Blood-pressure Monitoring System Based on the Volume-compensation Method

Development of a Finger Cuff Unit for a Noninvasive Blood-pressure Monitoring System Based on the Volume-compensation Method

Non-invasive beat-to-beat determination of changes in the small artery compliance after smoking.

We investigated the response of the small arterial compliance on smoking in 5 occasional smokers before, during and after inhaling the first cigarette in the day. For this purpose we used a non-invasive method based on interpretation of the oscillometric signal from the finger cuff coupled to the signal from photoplethysmograph. This system enables on-line determination of the finger artery compliance as function of transmural pressure (ptm) between 0 and 120 mmHg, where each heart beat is presented by a set of compliance values in the range of the pulse pressure reduced by the cuff pressure. This procedure allowed construction of time course of the arterial compliance. When comparing the compliance value at ptm of 40 mmHg, we found its fluctuations around the steady value during the rest and immediate lowering of the compliance after smoking, accompanied by the increase of blood pressure and heart rate.

Ultrasound probe having interchangeable accessories

In the present invention, an intraoperative ultrasound transducer probe, or intraoperative probe, has a housing, to which, interchangeable accessories may be attached. The interchangeable accessories adapt the intraoperative probe's shape to provide access to a patient's body parts in confined spaces in intraoperative environments. In one embodiment of the present invention a first interchangeable accessory has an extension handle that may be attached to the intraoperative probe to enable an operator to reach into surgical incisions and view the patient's body parts. In an alternate embodiment of the present invention a second interchangeable accessory has a finger cuff for attaching the intraoperative probe to an operator's finger. The finger cuff may be used in place of the extension handle, providing access to a patient's body parts in confined spaces, such as the posterior side of the heart for epicardial imaging during open heart surgery. Since the interchangeable accessories are separable from the intraoperative probe, they are easily sterilized and may be disposed of after use. The interchangeable accessories used to adapt the intraoperative probe's shape have low manufacturing cost relative to the cost of multiple dedicated probes, reducing the overall cost of an ultrasound imaging system.

Use of a neonatal blood pressure cuff to monitor blood pressure in the adult finger--comparison with a standard adult arm cuff.

There are few suitable methods for monitoring blood pressure continuously (or intermittently) for research in adult stroke patients, who are ill but do not justify invasive intensive care monitoring. We tested a neonatal arm blood pressure in adults by placing it on the forefinger ("finger cuff"). We compared the repeatability of the finger cuff with blood pressure measured by a standard adult arm cuff using the oscillometric technique in 168 ambulatory outpatients attending a cerebrovascular disease clinic. The mean difference between sequential mean blood pressure readings with the finger cuff was 0.55 mm Hg (95% confidence interval (CI) -14.36 to 15.47 mm Hg), and for the arm cuff was 3.31 mm Hg (95% CI -23.33 to 16.71 mm Hg). Measurements made with the arm cuff were shown to affect subsequent arm cuff readings made within a few minutes of the first. The mean difference between the finger cuff and arm cuff mean blood pressure readings was 0.03 mm Hg (95% CI -26.07 to 26.14 mm Hg) and agreement was better when the blood pressure was measured with the finger cuff first rather than the arm cuff. However, although there was no difference in the mean blood pressure recordings both systolic and diastolic blood pressure measurements differed systematically between arm and finger cuff. The reproducibility of sequential blood pressure measurements made with the finger cuff was better than with the arm cuff. The performance of the finger cuff compared with that of the arm cuff was sufficiently good to encourage use of the finger cuff in research involving automatic intermittent monitoring to observe sequential blood pressures over time in stroke patients. However, measurements of systolic and diastolic pressure were not the same with the two cuffs and further work on calibration of the finger cuff would be useful.

Accuracy and reliability of noninvasive continuous finger blood pressure measurement in critically ill patients.

To evaluate the accuracy and reliability of noninvasive continuous finger blood pressure measurement in critically ill patients. Prospective data collection. Emergency department in a 2,000-bed hospital. Thirty-nine patients admitted to the emergency department requiring invasive arterial blood pressure monitoring were enrolled to the study protocol. Continuous noninvasive blood pressure measurement was performed on the middle phalanx of the second and third finger, using a test instrument which provides continuous arterial waveform display with the use of a finger cuff. Invasive mean arterial blood pressure measurement was done by cannulation of the radial artery and direct transduction of the systemic arterial pressure waveform. Three thousand one hundred eighteen pairs of simultaneous finger cuff and intra-arterial blood pressure measurements were collected in 1-min intervals from 39 patients over a total of 51.8 hrs. The overall discrepancy between both measurements was 0.10 mm Hg. The standard deviation of the differences was +/- 5.02 mm Hg. The mean bias in patients treated with catecholamines was 0.01 mm Hg and was not different from the bias observed in patients without catecholamines (mean bias: 0.23 mm Hg; p > .22). Whereas 95% of all comparisons between finger cuff and intra-arterial measurement had a discrepancy < or = +/- 10 mm Hg, 4.7% had a discrepancy between +/- 10.1 to 15 mm Hg and 0.3% exhibited a discrepancy > +/- 15 mm Hg. In 29 (74%) patients, the duration of errors > 10 mm Hg was < or = 1 min. In seven (18%) patients, the duration of errors > 10 mm Hg was between 2 to 3 mins and in three (8%) patients, the errors lasted for > 3 mins. Our data provide a guide to the accuracy and reliability of noninvasive finger blood pressure measurements in critically ill patients. Although most test instrument measurements were reliable, in 8% of all patients large discrepancies (> 10 mm Hg) between both measurements with a duration of > 3 mins were noted. Concerning the considerable risk for arterial cannulation, our preliminary data demonstrate that the test instrument (PORTAPRES, TNO Biomedical Instrumentation Research Unit; The Netherlands) is an advance in noninvasive monitoring of critically ill patients and may be useful in most emergency clinical settings.

ENHANCED BLOOD FLOW RESPONSE DURING REACTIVE HYPEREMIA IN HUMANS WITH PROSTAGLANDIN INHIBITION 1048

The hypothesis that vasodilatory prostaglandins contribute to the reactive hyperemia observed following ischemic exercise was tested in 4 male volunteers. Subjects performed 5 min of handgrip exercise while blood flow was occluded with an inflatable cuff to 250 mmHg. Continuous measures of mean blood velocity (MBV; pulsed Doppler), brachial artery diameter (D; echo Doppler), and mean perfusion blood pressure (MPP; Finapres finger cuff) were collected during 1 min of rest, 5 min of ischemic exercise, and 10 min of recovery rest. Brachial artery blood flow (MBV · πr2), and vascular conductance (BF/MPP) were calculated for 15, 30, 45, 90, 120, 240 and 360 s of recovery. The exercise was performed without (C) and with (IBU) oral administration of ibuprofen (1200 mg/d for 2 d). Compared with C, vascular responses in IBU tended to be greater at all time points and were significantly greater at 120 and 240 s of recovery; the results at 120 s were as follows: Table The significant increases in VC, MBV and BF with IBU all argue against the hypothesis of prostaglandin-mediated vasodilation. The mechanism responsible for this unexpected finding warrants further study.

Faster femoral artery blood velocity kinetics at the onset of exercise following short-term training

Objective: The hypothesis that the adaptation to endurance exercise training included a faster increase in blood flow at the onset of exercise was tested in 12 healthy young men who endurance-trained (ET) 2 h/day, for 10 days at 65% V̇O2 peak on a cycl and in 11 non-training control (C) subjects. Methods: Blood flow was estimated from changes in femoral artery mean blood velocity (MBV) by pulsed Doppler. Beat-by-beat changes in cardiac output (CO) and mean arterial pressure (MAP) were obtained by impedance cardiography and a Finapres finger cuff, respectively. MBV, MAP and CO were measured at rest and during 5 min of dynamic knee extension exercise. Both legs worked alternately with 2 s raising and lowering a weight (15% maximal voluntary contraction) followed by 2 s rest while the other leg raised and lowered the weight. Results: In the ET group the time to 63% (T63%) of the approximately exponential increase in MBV following 10 days of training (8.6 ± 1.2 s, mean ± s.e.) was significantly faster than the Day 0 response (14.2 ± 2.1 s, P < 0.05). The T63% of femoral artery vascular conductance (VCfa) was also faster following 10 days of ET (9.4 ± 0.9 s) versus Day 0 (16.0 ± 2.5 s) (0.05). There was no change in the T63% of both MBV and VCfa for the C group. The kinetics of CO were not significantly affected by ET, but the amplitude of CO in the adaptive phase, and at steady state, were significantly greater (P < 0.05) at Day 10 compared to Day 0 for the ET group with no change in the C group. Conclusions: These data supported the hypothesis that endurance training resulted in faster adaptation of blood flow to exercising muscle, and further showed that this response occurred early in the training program.

Faster femoral artery blood velocity kinetics at the onset of exercise following short-term training

The hypothesis that the adaptation to endurance exercise training included a faster increase in blood flow at the onset of exercise was tested in 12 healthy young men who endurance-trained (ET) 2 h/day, for 10 days at 65% VO2 peak on a cycle ergometer, and in 11 non-training control (C) subjects. Blood flow was estimated from changes in femoral artery mean blood velocity (MBV) by pulsed Doppler. Beat-by-beat changes in cardiac output (CO) and mean arterial pressure (MAP) were obtained by impedance cardiography and a Finapres finger cuff, respectively. MBV, MAP and CO were measured at rest and during 5 min of dynamic knee extension exercise. Both legs worked alternately with 2 s raising and lowering a weight (15% maximal voluntary contraction) followed by 2 s rest while the other leg raised and lowered the weight. In the ET group the time to 63% (T63%) of the approximately exponential increase in MBV following 10 days of training (8.6 +/- 1.2 s, mean +/- s.e.) was significantly faster than the Day 0 response (14.2 +/- 2.1 s, P < 0.05). The T63% of femoral artery vascular conductance (VCfa) was also faster following 10 days of ET (9.4 +/- 0.9 s) versus Day 0 (16.0 +/- 2.5 s) (0.05). There was no change in the T63% of both MBV and VCfa for the C group. The kinetics of CO were not significantly affected by ET, but the amplitude of CO in the adaptive phase, and at steady state, were significantly greater (P < 0.05) at Day 10 compared to Day 0 for the ET group with no change in the C group. These data supported the hypothesis that endurance training resulted in faster adaptation of blood flow to exercising muscle, and further showed that this response occurred early in the training program.

763-2 Attenuated Contractile Reserve in Chronic Severe Heart Failure: Evaluation by Automated Noninvasive Pressure-Volume Relations and Dobutamine Echocardiography

To determine LV contractile reserve in pts with chronic severe heart failure (CHF), automated estimates of LV volume and noninvasive arterial pressure were used to generate on-line pressure-volume loops. Seven CHF pts, (aged 45 ± 101 with mean LVEF 21 ± 6% and 10 normal subjects, (aged 32 ± 3 yrs) with LVEF 56 ± 5% were studied at baseline and during graded dobutamine infusion at 5, 7.5 and 10 μ g/kg/min. LVvolume (4-chamber view Simpson's rule) by echo automated border detection and noninvasive arterial pressure using a finger cuff photoplethysmograph were used to construct arterial pressure — LV volume loops. Stroke work (SW), ∫pressure d volume, was estimated with an assumed LV diastolic pressure of 20 mmHg for CHF pts and 10 mmHg for controls. Examples and mean ± SD SW are shown. Significant differences in baseline LV function were observed between groups. Graded increases in SW occurred with dobutamine inotropic modulation in both groups, although the responses were significantly attenuated in CHF pts (p &lt; 0.05). This noninvasive method may be useful to assess LV contractile reserve in chronic CHF pts.

Heart rate and blood pressure variability in subjects exposed to simulated increases in gravity

The effect of simulated increases in gravity (G) force on blood pressure and heart rate variability was investigated in seven normal healthy subjects using a man-carrying centrifuge. Subjects were exposed to G forces up to 3.6 times the gravity at the earth's surface (3.6 G). Blood pressure was measured non-invasively using a finger cuff (Finapres), while the subjects breathed at a fixed rate and depth. The blood pressure waveform was digitized and systolic blood pressure, diastolic blood pressure and beat-to-beat intervals were extracted from these data. Power spectra were produced from these values. Increases in G force produced increases in spectral power of systolic blood pressure and diastolic blood pressure at the respiratory frequency (0.2 Hz) and less conspicuous but significant increases in spectral power at lower frequencies (0.045-0.15 Hz). The spectral power of beat-to-beat interval did not change. It is postulated that the reduction in central blood volume produced by increased gravity is affecting blood pressure control in a similar way to that seen in hypovolaemic animals. The marked increase in blood pressure fluctuations induced by respiration at the higher G levels may be a result of the alteration in venous return to the right atrium, ultimately reflected as fluctuating left ventricular output and pressure.

The Finapres 2300e finger cuff

Blood pressure measurements associated with malapplication of a finger cuff were compared with contemporaneous intra-arterial pressure data in seven volunteers to determine the influence of cuff application on the accuracy of the Finapres 2300e. Systolic readings in all cuff positions differed from arterial line data by more than the recommended standard and tight and loose cuff applications under and over-read respectively, in all subjects. The results show the Finapres to be sensitive to small degrees of finger cuff malapplication which contribute to the bias on direct arterial comparison and limit the reliability of the instrument in clinical practice.

Continuous direct and indirect blood pressure measurement (Finapres) in the critically ill

Continuous noninvasive blood pressure measurement is of great potential use in the critically ill. This study was designed to find out whether measurements of blood pressure by a Finapres accurately represented intra-arterial pressure. Comparisons were made between readings from a radial artery line and from a Finapres finger cuff in 10 critically ill patients. There was an unpredictable but usually stable difference between measurements from the two sources; this difference varied in magnitude and direction in individual patients. At present the Finapres cannot be recommended as a substitute for intra-arterial blood pressure measurement in the critically ill.

Rapid resetting of human baroreflex working range: insights from sympathetic recordings during acute hypoglycaemia.

1. Human muscle nerve sympathetic activity (MSA), which is governed by baroreflexes and involved in blood pressure homeostasis, is increased during acute insulin-induced hypoglycaemia. 2. To elucidate the detailed relationship between MSA and blood pressure during hypoglycaemia, 0.15 i.u. (kg body weight)-1 regular human insulin was given intravenously to eight fasting, healthy volunteers. Microneurographic recording of MSA in the peroneal nerve was made with simultaneous monitoring of arterial blood pressure by a finger cuff (Finapres). The course of MSA and blood pressure was monitored for 30 min before and 60 min after insulin injection. In three subjects control recording without insulin injection was made for the same duration. 3. Stimulus-response regression lines were constructed by plotting diastolic blood pressure against the occurrence frequency of MSA for the period of initial rest, the period of maximal MSA outflow during hypoglycaemia and the period of glucose counter-regulation. The control experiments were analysed for the corresponding periods. 4. The stimulus-response line was stable throughout the control experiments, whereas it was shifted either to the left or to the right during hypoglycaemia, and regularly shifted to the left (i.e. towards a lower blood pressure) during glucose counter-regulation, without change of slope. 5. It is concluded that the changes in MSA during acute hypoglycaemia are not secondary to baroreflex regulation but instead are characterized by acute resetting of the baroreflex working range without change of sensitivity.

Cardiac output, oxygen consumption and arteriovenous oxygen difference following a sudden rise in exercise level in humans.

1. To investigate the relative contributions of increases in cardiac output and arteriovenous oxygen difference to the increase in oxygen consumption during exercise, the ventilatory and cardiovascular responses to a sudden transition from unloaded cycling to 70 or 80 W were measured in six normal healthy subjects. 2. Oxygen consumption (VO2) was measured breath-by-breath and corrected for changes in lung gas stores. Cardiac output (Q) was measured beat-by-beat using pulsed Doppler ultrasound, and blood pressure was measured beat-by-beat using a non-invasive finger cuff (Finapres). All data were calculated off-line, second-by-second. 3. Arteriovenous oxygen difference (A-VO2) was calculated from Q and VO2 using the Fick Principle. Left ventricular afterload was calculated by dividing Q by mean blood pressure. 4. The data for Q and VO2 were closely fitted by single exponential curves (mean r2 0.84 and 0.90 respectively; r is the correlation coefficient). These curves yielded mean time constants for the increases in Q and VO2 of 28 and 55 s respectively following the increase in exercise level. In each individual subject, the time course of adjustment of Q was faster than that of VO2. There was a mean lag of 15 s from the start of the new exercise level before the derived A-V O2 began to increase; the mean time constant for A-V O2 was 57 s. 5. If A-V O2 had remained constant, the observed rise in Q alone would have resulted in an average of 87% of the increase in VO2 which was observed after 5 s. If Q had remained constant, the observed increase in A-V O2 would have led to only 8% of the actual increase in VO2 after 5 s. 6. Mean and systolic blood pressure rose and afterload fell immediately after the onset of the increased workload. The time constants of the systolic blood pressure and afterload responses to exercise varied widely and ranged from 37 to 81 and 10 to 26 s respectively (n = 4). 7. We conclude that Q is responsible for most of the early increase in VO2 following a sudden increase in exercise workload. Blood pressure responses to exercise are slower than Q and VO2 responses, probably due to the rapid decrease in afterload. 8. The dominant contribution of Q to adaptation to changing workload may be physiologically important particularly in heart disease, where decreased ability to increase cardiac output may limit the capacity to cope with changing metabolic needs during everyday activities.