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Biomedical subjects

G Antonutto

Publications and source records attributed to G Antonutto.

At least 19 recordsLinked to original sources
PubMed2006

Factors determining the time course of VO2(max) decay during bedrest: implications for VO2(max) limitation.

The aim of this study was to characterize the time course of maximal oxygen consumption VO2(max) changes during bedrests longer than 30 days, on the hypothesis that the decrease in VO2(max) tends to asymptote. On a total of 26 subjects who participated in one of three bedrest campaigns without countermeasures, lasting 14, 42 and 90 days, respectively, VO2(max) maximal cardiac output (Qmax) and maximal systemic O2 delivery (QaO2max) were measured. After all periods of HDT, VO2max, Qmax, and QaO2max were significantly lower than before. The VO2max decreased less than qmax after the two shortest bedrests, but its per cent decay was about 10% larger than that of Qmax after 90-day bedrest. The VO2max decrease after 90-day bedrest was larger than after 42- and 14-day bedrests, where it was similar. The Qmax and QaO2max declines after 90-day bedrest was equal to those after 14- and 42-day bedrest. The average daily rates of the VO2max, Qmax, and QaO2max decay during bedrest were less if the bedrest duration were longer, with the exception of that of VO2max in the longest bedrest. The asymptotic VO2max decay demonstrates the possibility that humans could keep working effectively even after an extremely long time in microgravity. Two components in the VO2max decrease were identified, which we postulate were related to cardiovascular deconditioning and to impairment of peripheral gas exchanges due to a possible muscle function deterioration.

Adaptation, Physiological↗
PubMed2005

Sprint running: a new energetic approach.

The speed of the initial 30 m of an all-out run from a stationary start on a flat track was determined for 12 medium level male sprinters by means of a radar device. The peak speed of 9.46+/-0.19 m s(-1) (mean +/- s.d.) was attained after about 5 s, the highest forward acceleration (a(f)), attained immediately after the start, amounting to 6.42+/-0.61 m s(-2). During acceleration, the runner's body (assumed to coincide with the segment joining the centre of mass and the point of contact foot terrain) must lean forward, as compared to constant speed running, by an angle alpha = arctang/a(f) (g = acceleration of gravity). The complement (90-alpha) is the angle, with respect to the horizontal, by which the terrain should be tilted upwards to bring the runner's body to a position identical to that of constant speed running. Therefore, accelerated running is similar to running at constant speed up an ;equivalent slope' ES = tan(90-alpha). Maximum ES was 0.643+/-0.059. Knowledge of ES allowed us to estimate the energy cost of sprint running (C(sr), J kg(-1) m(-1)) from literature data on the energy cost measured during uphill running at constant speed. Peak Csr was 43.8+/-10.4 J kg(-1) m(-1); its average over the acceleration phase (30 m) was 10.7+/-0.59 J kg(-1) m(-1), as compared with 3.8 for running at constant speed on flat terrain. The corresponding metabolic powers (in W kg(-1)) amounted to 91.9+/-20.5 (peak) and 61.0+/-4.7 (mean).

Acceleration↗
PubMed2004

Muscle-fiber conduction velocity estimated from surface EMG signals during explosive dynamic contractions.

Muscle-fiber conduction velocity (CV) was estimated from surface electromyographic (EMG) signals during isometric contractions and during short (150-200 ms), explosive, dynamic exercises. Surface EMG signals were recorded with four linear adhesive arrays from the vastus lateralis and medialis muscles of 12 healthy subjects. Isometric contractions were at linearly increasing force from 0% to 100% of the maximum. The dynamic contractions consisted of explosive efforts of the lower limb on a sledge ergometer. For the explosive contractions, muscle-fiber CV was estimated in seven time-windows located along the ascending time interval of the force. There was a significant correlation between CV values during the isometric ramp and explosive contractions (R = 0.75). Moreover, CV estimates increased significantly from (mean +/- SD) 4.32 +/- 0.46 m/s to 4.97 +/- 0.45 m/s during the increasing-force explosive task. It was concluded that CV can be estimated reliably during dynamic tasks involving fast limb movements and that, in these contractions, it may provide important information on motor-unit control properties.

Adult↗
PubMed2003

Cardiovascular deconditioning in microgravity: some possible countermeasures.

Microgravity is an extreme environment inducing relevant adaptive changes in the human body, especially after prolonged periods of exposure. Since the early sixties, numerous studies on the effects of microgravity, during manned Space flights, have produced an increasing amount of information concerning its physiological effects, globally defined "deconditioning". Microgravity deconditioning of the cardiovascular system (CVD) is briefly reviewed. It consists of: (1) a decrease of circulating blood and interstitial fluid volumes, (2) a decrease of arterial blood diastolic pressure, (3) a decrease of ventricular stroke volume, (4) a decrease of the estimated left ventricular mass and (5) resetting of the carotid baroreceptors. The negative effects of microgravity deconditioning manifest themselves mostly upon the reentry to Earth. They consist mainly of: (1) dizziness, (2) increased heart rate and heart palpitations, (3) an inability to assume the standing position (orthostatic intolerance), (4) pre-syncopal feelings due to postural stress and (5) reduced exercise capacity. To avoid these drawbacks several countermeasures have been proposed; they will be briefly mentioned with emphasis on the "Twin Bikes System" (TBS). This consists of two coupled bicycles operated by astronauts and counter-rotating along the inner wall of a cylindrical Space module, thus generating a centrifugal force vector, mimicking gravity.

Algorithms↗
PubMed2000

Effects of different after-loads and knee angles on maximal explosive power of the lower limbs in humans.

Maximal explosive power during two-leg jumps was measured on four sedentary subjects [mean age 43.0 (SD 10.3) years, mean height 1.74 (SD 0.04) m, mean body mass 73.5 (SD 1.3) kg] using a sledge apparatus with which both force and speed could be directly measured. Different after-loads were obtained by positioning the sledge at five different angles (SA, alpha) in respect to the horizontal so that m x g x sin alpha (where m is the sum of body mass and the mass of the sledge seat, g the acceleration due to gravity) decreased (on average) from 78% body mass at 30 degrees to 27% body mass at 10 degrees, thus simulating conditions of low gravity. The subjects were asked to jump maximally, without counter movement, starting from 70 degrees, 90 degrees, 110 degrees, and 140 degrees of knee angle (KA); the protocol being repeated at 10 degrees, 15 degrees, 20 degrees, 25 degrees and 30 degrees SA. The average (W+(mean)) power output during concentric exercise (CE) was found to decrease when the starting KA was increased, but to be unaffected by SA (i.e. by the after-load, the simulated low g). The higher values of W+(mean) were recorded at 90 degrees KA [15.01 (SD 1.46) W x kg(-1), average for all subjects at all SA]. The subjects were also asked to perform counter movement (CMJ) and rebound jumps (RE) at the same SA as for CE. In CMJ and RE maximal power outputs were also found to be unaffected by the SA; W+(mean) amounted to 16.03 (SD 0.28) W x kg(-1) in CMJ and 16.88 (SD 0.36) W x kg(-1) in RE (average for all subjects at all SA). In CE, CMJ and RE, the instantaneous force at the onset of the positive speed phase (F(i)) was found to increase linearly with SA (i.e. with increasing m x g x sin alpha), and the difference between F(i) in CMJ or RE and F(i) in CE (F(i) in CMJ minus F(i) in CE and F(i) in RE minus F(i) in CE) was unaffected by SA. This indicated that both maximal power and the elastic recoil were unaffected by simulated low g ranging from 1.71 m x s(-2) (at 10 degrees SA) to 4.91 m x s(-2) (at 30 degrees SA).

Adult↗
PubMed2000

The hemodynamic and metabolic effects of tourniquet application during knee surgery.

UNLABELLED: We evaluated the effects of tourniquet application on the cardiovascular system and metabolism in 10 young men undergoing knee surgery with general anesthesia. The duration of inflation was from 75 to 108 min. Heart rate, mean arterial pressure, cardiac index (CI) by pulse contour method, and systemic vascular resistance were measured before, during, and after tourniquet inflation. pH, PaO(2), PaCO(2), and lactate blood concentrations were also measured. VO(2) and VCO(2) were assessed every minute from tracheal intubation up to 15 min after tourniquet deflation and VO(2) in excess of the basal value over the 15 min after deflation (VO(2)exc) was calculated. Mean arterial pressure increased 26% (P: < 0.05) during inflation and returned to basal values after deflation. CI did not change immediately after inflation; although, thereafter, it increased 18% (P: < 0.05). Five minutes after deflation, CI further increased to a value 40% higher than the basal value. Therefore, systemic vascular resistance increased 20% suddenly after inflation (P: < 0.05) and decreased 18% after deflation (P: < 0.05). VO(2) and VCO(2) remained stable during inflation and increased (P: < 0.05) after deflation. VO(2)exc depended on duration of tourniquet inflation time (Tisch) (P: < 0.05). After deflation, PaCO(2) and lactate increased (P: < 0.05) while Tisch increased. We conclude that tourniquet application induces modifications of the cardiovascular system and metabolism, which depend on tourniquet phase and on Tisch. Whether these modifications could be relevant in patients with poor physical conditions is not known. IMPLICATIONS: The clinical effects of tourniquet application were evaluated in 10 young men undergoing knee surgery. Our data indicate that tourniquet application causes hemodynamic and metabolic changes which may become clinically relevant after a long period of tourniquet inflation, particularly in patients with concomitant cardiovascular diseases.

Adolescent↗
PubMed1999

Effects of microgravity on maximal power of lower limbs during very short efforts in humans.

The maximal power of the lower limbs was determined in four astronauts (age 37-53 yr) 1) during maximal pushes of approximately 250 ms on force platforms ["maximal explosive power" (MEP)] or 2) during all-out bouts of 6-7 s on an isokinetic cycloergometer [pedal frequency 1 Hz: maximal cycling power (MCP)]. The measurements were done before and immediately after spaceflights of 31-180 days. Before flight, peak and mean values were 3.18 +/- 0.38 and 1.5 +/- 0. 13 (SD) kW for MEP and 1.17 +/- 0.12 and 0.68 +/- 0.08 kW for MCP, respectively. After reentry, MEP was reduced to 67% after 31 days and to 45% after 180 days. MCP decreased less, attaining approximately 75% of preflight level, regardless of the flight duration. The recovery of MCP was essentially complete 2 wk after reentry, whereas that of MEP was slower, a complete recovery occurring after an estimated time close to that spent in flight. In the same subjects, the muscle mass of the lower limbs, as assessed by NMR, decreased by 9-13%, irrespective of flight duration (J. Zange, K. Müller, M. Schuber, H. Wackerhage, U. Hoffmann, R. W. G unther, G. Adam, J. M. Neuerburg, V. E. Sinitsyn, A. O. Bacharev, and O. I. Belichenko. Int. J. Sports Med. 18, Suppl. 4: S308-S309, 1997). The larger fall in maximal power, compared with that in muscle mass, suggests that a fraction of the former (especially relevant for MEP) is due to the effects of weightlessness on the motor unit recruitment pattern.

Adult↗
PubMed1998

Effects of prolonged bed rest on cardiovascular oxygen transport during submaximal exercise in humans.

The hypothesis was tested that prolonged bed rest impairs O2 transport during exercise, which implies a lowering of cardiac output Qc and O2 delivery (QaO2). The following parameters were determined in five males at rest and at the steady-state of the 100-W exercise before (B) and after (A) 42-day bed rest with head-down tilt at -6 degrees: O2 consumption (VO2), by a standard open-circuit method; Qc, by the pressure pulse contour method, heart rate (fc), stroke volume (Qh), arterial O2 saturation, blood haemoglobin concentration ([Hb]), arterial O2 concentration (CaO2), and QaO2. The VO2 was the same in A and in B, as was the resting fc. The fc at 100 W was higher in A than in B (+17.5%). The Qh was markedly reduced (-27.7% and -22.2% at rest and 100 W, respectively). The Qc was lower in A than in B [-27.6% and -7.8% (NS) at rest and 100 W, respectively]. The CaO2 was lower in A than in B because of the reduction in [Hb]. Thus also QaO2 was lower in A than in B (-32.0% and -11.9% at rest and at 100 W, respectively). The present results would suggest a down-regulation of the O2 transport system after bed rest.

Adult↗
PubMed1998

Maximal power and EMG of lower limbs after 21 days spaceflight in one astronaut.

Long term space flights affect negatively muscle structure and function (Grigoriev end Egorov, 1901, 1902; Edgerton and Roy, 1994; Jaweed, 1994; Nicogossian, 1994a; Antonutto et al., 1995, Edgerton and Roy, 1997), essentially because of the long-term exposure to microgravity. Indeed, we have previously shown that the average power developed during a very short (approximately 0.25 s) maximal effort of the lower limbs, such as a vertical jump off both feet ("maximal explosive power", MEP) was reduced to 67% of pre-flight values after one month in microgravity (one subject) and to 45% after six months (three subjects). The reductions of MEP was larger than the concomitant decrease of muscle mass (9 to 13%, Zange et al., 1997). This suggests that a substantial fraction of the decrease of maximal power is due to the deterioration of the motor control, brough about by the absence of gravity. The aim of the present study was to investigate further the effects of microgram on maximal muscular power assessing also the EMG activities of 3 heads of the quadriceps femoris muscle, which contributes the major share of MEP.

Acceleration↗
PubMed1998

[Non-invasive evaluation of cardic output by analysis of peripheral pressure profile in patients recovering in intensive care].

BACKGROUND: The analysis of the arterial pulse contour obtained by means of a non-invasive device (Finapres) seems to be an ideal method to measure cardiac output (CO). An individual calibration factor (Z) dimensionally equal to aortic impedence is the necessary pre-requisite to calculate CO by pulse contour analysis. To verify the reliability of non-invasive pulse contour method, we compared the COs measured from Finapres tracings with those measured from thermodilution method in Intensive Care patients. METHODS: In 9 patients undergoing cardiac and general surgery, CO was measured from thermodilution (COTD) within 24 hours of postoperative period (total of 67 measurements). During COTD measurements, Finapres tracings were recorded and then analysed to calculate CO by two different procedures. In the former (COA), Z was calculated from an algorithm which takes into account heart rate, mean arterial pressure and age of the patient. In the latter procedure (COB), Z was experimentally determined from the initial COTD measure and then updated for the hemodynamic conditions of the patient. RESULTS: COTD ranged between 3.5 and 9.5 L.min-1 (mean value 5.53 +/- 1.29 L.min-1). The mean difference between COTD e COA was 0.485 +/- 1.537 L.min-1 and the mean percentage error was 25.1 +/- 14.5%. The experimental determination of Z reduced the mean difference and the mean percentage error between thermodilution and Finapres method to--0.002 +/- 1.056 L.min-1 and 15.5 +/- 11.0%, respectively. The regression line between COTD and COB turned out to be: COB = 0.68 + 0.88.COTD (r = 0.73). CONCLUSIONS: The pulse contour analysis applied to Finapres tracing allows to calculate CO with reasonable accuracy in the intensive care patients. An initial experimental determination of Z is recommended to improve the accuracy of Finapres method.

Adult↗
PubMed1997

The interplay of central and peripheral factors in limiting maximal O2 consumption in man after prolonged bed rest.

1. The effects of bed rest on the cardiovascular and muscular parameters which affect maximal O2 consumption (VO2,max) were studied. The fractional limitation of VO2,max imposed by these parameters after bed rest was analysed. 2. The VO2,max, by standard procedure, and the maximal cardiac output (Qmax), by the pulse contour method, were measured during graded cyclo-ergometric exercise on seven subjects before and after a 42-day head-down tilt bed rest. Blood haemoglobin concentration ([Hb]) and arterialized blood gas analysis were determined at the highest work load. 3. Muscle fibre types, oxidative enzyme activities, and capillary and mitochondrial densities were measured on biopsy samples from the vastus lateralis muscle before and at the end of bed rest. The measure of muscle cross-sectional area (CSA) by NMR imaging at the level of biopsy site allowed computation of muscle oxidative capacity and capillary length. 4. The VO2,max was reduced after bed rest (-16.6%). The concomitant decreases in Qmax (-30.8%), essentially due to a change in stroke volume, and in [Hb] led to a huge decrease in O2 delivery (-39.7%). 5. Fibre type distribution was unaffected by bed rest. The decrease in fibre area corresponded to the significant reduction in muscle CSA (-17%). The volume density of mitochondria was reduced after bed rest (-16.6%), as were the oxidative enzyme activities (-11%). The total mitochondrial volume was reduced by 28.5%. Capillary density was unchanged. Total capillary length was 22.2% lower after bed rest, due to muscle atrophy. 6. The interaction between these muscular and cardiovascular changes led to a smaller reduction in VO2,max than in cardiovascular O2 transport. Yet the latter appears to play the greatest role in limiting VO2,max after bed rest (> 70% of overall limitation), the remaining fraction being shared between peripheral O2 diffusion and utilization.

Adult↗
PubMed1997

Effects of elastic recoil on maximal explosive power of the lower limbs.

The maximal explosive power during a two legs jump was measured on four competitive athletes [mean age 24(SD 4.3) years; height 1.79 (SD 0.09) m; body mass 68.7 (SD 12.8) kg] at different starting knee angles (70, 90, 110, 130 and 150 degrees). The experiments were performed on a newly developed instrument with which both force and speed could be measured using a force platform and a wire tachometer, respectively, and on a conventional force platform. At the smallest knee angle (70 degrees) the mean power output (W in watts per kilogram) developed during the jump was found not to differ significantly between the two methods (P > 0.1). At the larger knee angles W was 18.4% (90 degrees), 34.5% (110 degrees), 47.4% (130 degrees) and 19.4% (150 degrees) higher using the conventional force platform (P < 0.05 throughout). The difference of W between the two methods was attributed to the recovery of elastic energy due to the counter movement which immediately preceded the jump on the conventional platform, but not on the newly developed instrument. Indeed because of a mechanical arrangement which prevented the subject from moving towards the platforms, eccentric work (W-) could not be performed on the newly developed instrument; whereas W- on the conventional force platform was almost negligible at 70 degrees knee angle [mean 1.7 (SD 2.3 J)] reached a maximum of 13.1 (SD 7.9) J at 130 degrees and decreased again to a mean 4.7 (SD 3.6) J for the largest angle (150 degrees). Furthermore, on the conventional force platform, the force at the onset of the positive speed phase (Fi) was an increasing function of W- (r2 = 0.519, P < 0.001); and the difference of W between the conventional and new instruments was larger the larger the difference of Fi (r2 = 0.391, P < 0.01).

Adult↗
PubMed1996

The effect of laparoscopic cholecystectomy on cardiovascular function and pulmonary gas exchange.

Hemodynamic changes, pulmonary CO2 elimination (VECO2) and gas exchange were evaluated during laparoscopic cholecystectomy. An algorithm to calculate inspired ventilation (VI) needed to maintain constant PaCO2 was also developed. In 12 ASA physical status I patients undergoing laparoscopic cholecystectomy, heart rate (HR), mean arterial pressure (MAP), cardiac index (CI), and systemic vascular resistance index (SVRI) were measured by the analysis of a radial artery pressure profile before, during, and after CO2 insufflation. Alveolar-arterial oxygen pressure gradient (P(A-a)O2), physiological and alveolar ventilatory dead space fractions (VDphys/VT; VDalv/VT), and PaCO2 were measured as well. VECO2 was assessed every minute in the patients maintained in the head-up position. HR did not significantly change during pneumoperitoneum, whereas MAP showed a transient increase (24.9%; P < 0.05) after CO2 insufflation. CI remained stable during pneumoperitoneum, but increased (25.0%; P < 0.05) after deflation. As a consequence, SVRI transiently increased after CO2 insufflation and decreased by 15.8% (P < 0.05) 5 min after deflation. P(A-a)O2 increased slightly (P < 0.05) with increased anesthesia time. VDphys/VT and VDalv/VT did not change after pneumoperitoneum onset, but VDalv/VT decreased after CO2 deflation (13.4%; P < 0.05). VECO2 increased (decreased) after a monoexponential time course during (after) CO2 insufflation in 8 of 12 patients. The mean time constants (t) of the monoexponential functions were 26.3 and 15.4 min during and after pneumoperitoneum. A monoexponential time course was shown also by PaCO2 during CO2 insufflation (tau = 27.8 min). Finally, the VI needed to maintain PaCO2 at a selected value could be calculated by the following algorithm: VI = [0.448.(1-e(-t/tau) + 2.52].(VA.PaCO2.713)-1, where VA corresponds to alveolar ventilation and t must be chosen according to the pneumoperitoneum phase. We conclude that CO2 insufflation in the abdominal cavity does not induce significant changes in cardiopulmonary function in ASA physical status I patients. The algorithm proposed seems to be a useful tool for the anesthesiologists to maintain constant PaCO2 during all surgical procedures.

Adult↗
PubMed1996

Effects of body size, body density, gender and growth on underwater torque.

Two forces act on a human body motionless in water: weight (W) and buoyancy (B). They are applied to the center of mass (CM) and to the center of volume (CV) of the subject, respectively. CM and CV do not coincide; this generates a torque that is a measure of the tendency of the upper part of the body to rise, rotating around its center of mass. To quantify this tendency, Pendergast & Craig defined 'underwater torque' (T') as the product of the net force with which the feet of a subject lying horizontally in water tend to sink, times the distance between the feet and the center of volume of the lungs. In this paper we have investigated: (a) the relationships between T' and body weight (BW), height (H), body surface area (BS), body density (BD) and leg density (LD) in a group of 30 subjects (group A, 14 females and 16 males, age range 16-50 years); and (b) the effect of gender and growth on T' in a group of 110 subjects (group B, 67 girls and 43 boys, age range 12-17 years). In group A, T' was found to be linearly related with BW (r=0.833, P<0.001), H (r=0.803, P<0.001), BS (r=0.866, P<0.001), BD (r=0.617, P<0.001) and LD (r=0.549, P<0.005). A multiple linear regression analysis showed that BS and BD explained about 85% of the variability of T' (r2=0.85). In group B, T' was found to increase linearly with age (r=0.47, P<0.01), the increasing rate being three times higher in boys compared with girls. As a consequence, the T' ratio between boys and girls increased with age, from 1.69 at 13 years to 2.04 at 16 years.

Adolescent↗
PubMed1996

Blood pressure and heart rate responses to sudden changes of gravity during exercise.

Heart rate (HR) and blood pressure responses to sudden changes of gravity during 80- to 100-W leg exercise were studied. One group was exposed to sudden changes between 1.0 and 0 g in the head-to-foot direction (Gz+), starting upright and with repeated 30-s tilts to the supine position. Another group was exposed to sudden Gz+ changes between 1.8 and 0 g in an aircraft performing parabolic flight. Arterial blood pressure at the level of the carotid (carotid distending pressure, CDP) showed a large transient increase by 27-47 mmHg when Gz+ was suddenly decreased and a similar drop when Gz+ was suddenly increased. HR displayed a reverse pattern with larger transients (-22 to -26 min-1) in response to Gz+ decreases and more sluggish changes of lower amplitude in the other direction. Central blood volume, as estimated from the inverse of transthoracic impedance (1/TTI), varied in concert with Gz+. A model is proposed in which HR responses are described as a function of CDP and 1/TTI after a time delay of 2.3-3.0 s and including a low-pass filter function with time constants of 0.34-0.35 s for decreasing HR and time constants of 2.9-4.6 s for increasing HR. The sensitivity of the carotid component was around -0.8 to -1.0 min-1 . mmHg-1 (4-7 ms/mmHg). The cardiopulmonary baroreceptor component was an additive input but was of modest relative importance during the initial HR responses. For steady-state HR responses, however, our model suggests that inputs from carotid and cardiopulmonary receptors are of equal importance.

Adult↗
PubMed1995

Noninvasive assessment of cardiac output from arterial pressure profiles during exercise.

The stroke volume of the left ventricle (SV) was assessed in nine young men (mean age 22.2, ranging from 20 to 25 years) during cycle ergometer upright exercise at exercise intensities from 60 to 150 W (about 20% to 80% of individual maximal aerobic power). The SV was calculated from noninvasive tracings of the arterial blood pressure, determined from photoplethysmograph records and compared to the SV determined simultaneously by pulsed Doppler echocardiography (PDE). Given the relationship SV = As.Z-1 in which A(s) is the area underneath the systolic pressure profile (in millimetres of mercury and second), and Z (in millimetres of mercury and second per millilitre) is the apparent hydraulic impedance of the circulatory system, a prerequisite for the assessment of SV from the photoplethysmograph tracings is a knowledge of Z. The experimental value of Z (hereafter defined Z*) was calculated by dividing A(s) (from the finger photoplethysmograph) by SV as obtained by PDE. When the whole group of subjects was considered, Z* was not greatly affected by the exercise intensity: it amounted to 0.089 (SD 0.028; n = 36). The Z was also estimated independently of any parameter other than heart rate (HR), mean (MAP) and pulse (PP) arterial blood pressure obtained from the photoplethysmograph. A computerized statistical method allowed us to interpolate the experimental values of Z*, HR, PP and MAP by the equation Zm = a.(b + c.HR + d.PP + e.MAP)-1, thus obtaining the coefficients a to e. The mean percentage error between Zm (calculated from the coefficients obtained and Z* was 21.8 (SD 14.3)%. However, it was observed that, in a given subject, Z* was significantly affected by the exercise intensity. Therefore, to improve the estimate of Z a second algorithm was developed to update the experimental value of Z determined initially at rest (Zin). This updated value (Zcor) of Z was calculated as Zcor = Zin. [(f/(i + g.(HR/HRin) + h.(PP/PPin) + 1.(MAP/MAPin)], where HRin, PPin, MAPin, HR, PP, MAP are the above parameters at rest and during exercise, respectively. Also in this case, the coefficients f to 1 were determined by a computerized statistical method using Z* as the experimental reference. The values of Zcor so obtained allowed us to calculate SV from arterial pulse contour analysis as SVF = As.Z-1cor. The mean percentage error between the SVF obtained and the values simultaneously determined by PDE, was 10.0 (SD 8.7)%. It is concluded that the SV of the left ventricle, and hence cardiac output, can be determined during exercise from photoplethysmograph tracings with reasonable accuracy, provided that an initial estimate of SV at rest is made by means an independent high quality reference method.

Adult↗