Biomedical subjects

H Theres

Publications and source records attributed to H Theres.

At least 37 records · Page 2Linked to original sources

PubMed1999

Phase-related changes in right ventricular cardiac output under volume-controlled mechanical ventilation with positive end-expiratory pressure.

OBJECTIVE: To examine determinants of right ventricular function throughout the ventilatory cycle under volume-controlled mechanical ventilation with various positive end-expiratory pressure (PEEP) stages. DESIGN: Prospective observational animal pilot study. SETTING: Animal research laboratory at a university hospital. SUBJECTS: Eight healthy swine under volume- controlled mechanical ventilation. INTERVENTIONS: Flow probes were implanted in eight swine in order to continuously measure blood flow in the pulmonary artery and inferior vena cava. After a recovery phase of 14 days, the swine were subjected to various PEEP stages (0, 5, 10 cm H2O) during volume-controlled positive pressure ventilation. MEASUREMENTS AND MAIN RESULTS: Continuous flow measurement took place in the pulmonary artery and inferior vena cava. Data on standard hemodynamic parameters were additionally acquired. Respiration-phase-specific analysis of right ventricular cardiac output and of additional hemodynamic function parameters followed, after calculation of mean values throughout five respiration cycles. PEEP at 5 cm H2O led to significant decreases in inferior vena cava flow (4.1%), and in right ventricular cardiac output (5.2%); the respective decreases at PEEP 10 cm H2O were 13.9% and 18.3%. In the inspiration phase at PEEP 10 cm H2O, results revealed an overproportionally pronounced decrease in comparison with the expiration phase in inferior vena cava flow (-24.6% vs. -10%) and right ventricular cardiac output (-35% vs. -13.5%). This phenomenon is presumably caused by a PEEP-related increase in mean airway pressure by the amount of 10.7 cm H2O in inspiration. CONCLUSIONS: Increases in PEEP during volume-controlled mechanical ventilation leads to respiration-phase-specific reduction of right ventricular cardiac output, with a significantly pronounced decrease during the inspiration phase. This decrease in cardiac output should be taken into particular consideration for patients with already critically reduced cardiac output.

Airway Resistance↗

PubMed1999

Automatic and efficient R wave discrimination in the right atrium using a two-state hidden Markov model.

INTRODUCTION: Discrimination of far-field R waves from atrial events in atrial electrograms (EGMs) is problematic in present implantable pacing systems. Adjustments of atrial refractory periods and sensitivity settings are the only options, and they will not provide optimal performance in many patients. The reliable detection or rejection of R waves in atrial EGMs would avoid problems of atrial undersensing or oversensing, thus benefiting DDD patients by providing more reliable and specific atrial arrhythmia detection. In addition, detection of far-field R waves could allow a measurement of AV conduction time in AAI and aid in discrimination of supraventricular tachyarrhythmia from ventricular tachyarrhythmia. METHODS AND RESULTS: Both atrial and ventricular unipolar EGMs were collected from 25 patients undergoing pacemaker implant or replacement. An average of 141 seconds of intrinsic or VVI paced EGMs was recorded and post analyzed. A new two-state hidden Markov model (HMM) was developed specifically for far-field R wave and P wave discrimination in the atrium. The recorded patients' EGMs were analyzed using this model, and the sensitivity and positive predictivity of far-field R wave detection were evaluated. The collected atrial EGMs were visually examined and marked as the control for verification of the detection analysis. Far-field R wave detection using this model had an overall sensitivity of 94% +/- 9.4% and a positive predictivity of 98.3% +/- 4.4%; and the far-field R wave rejection using the same model had a sensitivity and a positive predictivity of 98.8% +/- 3.8% and 99.1% +/- 1.7%, respectively. CONCLUSION: Far-field R wave detection in the right atrium by the two-state HMM is reliable and accurate, and can significantly improve atrial arrhythmia management for patients.

Adolescent↗

PubMed1999

Management of patients with acute myocardial infarction at five academic medical centers: clinical characteristics, resource utilization, and outcome.

BACKGROUND: Although variability in management of cardiovascular syndromes has been demonstrated among regions, the extent to which variability exists among academic medical centers in different countries in uncertain. METHODS: This retrospective cohort study includes data on consecutive patients (n = 694) with acute myocardial infarction who were admitted to five teaching hospitals from different countries (84, Brigham and Women's Hospital, USA; 97, Iizuka Hospital, Japan; 64, Hospital de Clinicas de Porto Alegre, Brazil; 62, Universitätsklinikum Charité, Germany; and 387, Hôpital Cantonal Universitaire de Genève, Switzerland) during a one-year period. Data were collected via chart review on clinical characteristics, rates of diagnostic and therapeutic interventions, complications and mortality, length of stay, and one-year follow-up outcomes. RESULTS: Patients' clinical characteristics varied among these institutions, with the lowest prevalence of antero-septal myocardial infarction at the US hospital. The US hospital had the lowest rate of use of thrombolytic therapy and did not have the highest rate for any invasive procedure. Average length of stay ranged from 7.7 +/- 4.3 days in the US hospital to 47.2 +/- 27.9 days in the Japanese hospital. There were no differences in one-year mortality among the four institutions (4% to 8%, P = 0.881) for which data were available. CONCLUSIONS: In this nonrandom sample of academic medical centers, the use of aggressive therapies for acute myocardial infarction was at least as common at non-US as US hospitals. Length of stay was much shorter at the US hospital. Despite these variations in management, evidence for differences in outcomes at one year were not detected.

Academic Medical Centers↗

PubMed1998

Electrophysiological properties of mechanosensitive atrial fibroblasts from chronic infarcted rat heart.

Electrically non-excitable but mechanosensitive right-atrial fibroblasts are thought to be involved in the chronotropic response of the heart to stretch. After myocardial infarction, altered chronotropic response may be due to the remodeling process which also involves the right atrium. Remodeling is associated with the development of hypertrophy of cardiomyocytes and proliferation of fibroblasts. Electrical properties of atrial mechanosensitive fibroblasts from chronic infarcted hearts and their possible role for altered chronotropic response has not, to our knowledge, been studied until now. Thus, resting membrane potential as well as mechanically induced potential of fibroblasts, action potential (AP) of cardiomyocytes, spontaneous frequency and mechanical activity of preparations from the sinus node region were studied 10 weeks after myocardial infarction induced by ligation of the left coronary artery in rats. The prolongation of AP repolarization (increases in APD50 and APD90) correlated closely to the infarct size (IS) and the degree of hypertrophy, respectively. Along with increasing IS, membrane potentials of fibroblasts were shifted to more negative values, with a peak of frequency distribution at -15 mV (control and very small IS), at -35 mV (intermediate IS), and -55 mV (large IS), and spontaneous electrical activity was decreased. Membrane resistance of fibroblasts also correlated to IS and was eight-fold greater at large IS than in control. We hypothesize that, in the infarcted heart, increased membrane potential and membrane resistance of fibroblasts may alter electrical activity of neighbouring myocytes in the sinus-venosus region via intercellular electrical coupling.

Animals↗

PubMed1998

Decreased susceptibility of contractile function to hypoxia/reoxygenation in chronic infarcted rat hearts.

Cardiac hypertrophy is associated with modifications in Ca2+ transport processes, enzymes of energy metabolism and antioxidant capacity. It is unknown whether these changes occur in infarct-induced hypertrophy with regard to an altered susceptibility to ischemia/reperfusion injury. We examined changes in sarcoplasmic reticulum (SR) Ca2+ transport, creatine kinase (CK) system, and the antioxidant enzymes glutathionperoxidase (GSH-Px) and superoxide dismutase (SOD) in rats 6 weeks after infarction due to coronary ligation (MI). Phenotypic modifications v sham operation (SHAM) were related to the contractile response of hypertrophied papillary muscle to hypoxia/reoxygenation for 30 min each. Under aerobic conditions we observed in MI v SHAM: decreases in isometric contraction and relaxation rate, a reduced Vmax-equivalent of sarcomeric shortening, a faster twitch-to-twitch decay of post-rest potentiation (PRC) which correlated closely to the decrease in SR Ca2+ uptake (-25%), a decrease in CK activity (-20%), reduced CK-MI and CK-MM, increased CK-MB and CK-BB, and enhanced activities of SOD (40%) and GSH-Px (50%). During hypoxia, an initial increase in peak force (PF) was followed by a slower PF decline in MI v SHAM. Reoxygenation caused a recovery of PF to approximately 30% in both groups; rates of contraction and relaxation recovered better in MI. In SHAM but not MI, twitch-to-twitch decay of PRC was accelerated after reoxygenation v aerobic control. The results suggest that adaptive changes in SR Ca2+ handling, CK isoenzymes and antioxidant enzymes may contribute to higher resistance against reduced oxygen supply and reoxygenation in hypertrophy due to MI.

Animals↗

PubMed1998

Electrogram signals recorded from acute and chronic pacemaker implantation sites in pacemaker patients.

Electrogram signals recorded from typical pacemaker implantation sites may be useful for a variety of pacemaker system functions including pacemaker follow-up, atrial and ventricular sensing (event detection), and triggered electrogram storage. We quantified the electrical characteristics of pacemaker pocket electrograms using a subcutaneous electrode array (SEA) in a population of 48 patients undergoing initial or replacement pacemaker implantation. SEA recorded intrinsic R wave amplitudes measured peak to peak averaged 118 microV and 65 microV for the two recorded SEA electrograms and were significantly different (P < 0.001); paced R wave amplitudes averaged 180 microV and 110 microV. P wave amplitudes averaged 39 microV and 26 microV. No statistically significant difference in amplitudes were observed between acute versus chronic pacemaker pocket or indication for pacing (AV block, sick sinus syndrome). Signal to noise ratios, using R wave amplitude as signal, were lower in the SEA electrogram on average (11 dB) compared to the intracardiac electrogram (27 dB), but sufficient for diagnostic assessment. R wave/P wave ratios for SEA signals were lower than surface and intracardiac values 3.1 and 2.7 compared to a range of 6.2-9.8, indicating a relative enhancement of P waves to R waves in SEA signals. In summary, SEA electrograms are of sufficient amplitude and signal quality (signal to noise ratio) to hold promise for future implantable device features such as electrogram telemetry, enhanced sensing, and diagnostic data storage.

Adult↗

PubMed1998

The influence of sensor orientation on activity-based rate responsive pacing. Sensor Orientation Study Group.

Piezoelectric activity-based rate responsive pacemakers are commonly implanted with the sensor facing inward. This study was conducted to assess the safe and effective rate response of an activity-based rate responsive pacemaker implanted with the sensor facing outward. A comparison were made to a previously studied patient group with sensor facing inward. Patient and pacemaker data was collected at predischarge and 2-month follow-up. Two-minute hall walks in conjunction with programmer-assisted rate response assessment were utilized to standardize initial rate response parameter settings for both patient groups. At 2-month follow-up, sensor rate response to a stage 3 limited CAEP protocol was recorded. Adequate sensor rate response was achieved for both patient groups. No difference was noted in reported patient complications for both groups. A statistically significant difference in programmed rate response curve setting and activity threshold for the two groups was noted at 2-month follow-up. Adequate sensor rate response was achieved for a patient population implanted with an activity-based rate responsive pacemaker with sensor facing outward. In this orientation, one higher rate response curve setting and an activity threshold one value more sensitive were required on average when compared to the normal sensor orientation group.

Aged↗

PubMed1998

Autonomic effects of dipyridamole stress testing on frequency distribution of RR and QT interval variability.

Transient myocardial ischemia and associated changes in the autonomic nervous system may influence heart rate and ventricular repolarization to variable degrees. This study evaluated the effect of dipyridamole (DIP) induced ischemia on the autonomic balance by spectral analysis of RR and QT intervals variability. Patients with coronary artery disease undergoing DIP stress echocardiography were studied. From high resolution ECG recordings, RR and QT interval measurements were performed by a dynamic template-matching algorithm. A time-variant analysis was used to estimate power in the LF (0.05-0.15 Hz) and in the HF (0.15-0.4 Hz) band of RR and QT interval spectra. Patients were grouped in ischemic and nonischemic subgroups based on the echocardiographic detection of wall-motion abnormalities. In patients without ischemia (n = 28), DIP caused a decrease in LF power and an increase in HF power of the RR and QT interval variability, indicating concordant changes of both intervals. In contrast, patients with inducible ischemia (n = 11) showed a decrease in HF power of the RR interval spectra and an increase of HF power of QT interval spectra. Furthermore, LF power was increased for RR but decreased for QT interval spectra. Our study suggests that DIP induced ischemia causes a loss of autonomic coupling between heart rate and ventricular repolarization for sympathetic and parasympathetic activities. This lability in ventricular repolarization may constitute an arrhythmogenic substrate during acute ischemia in patients with coronary artery disease.

Algorithms↗

PubMed1997

Contractile function of papillary muscle from rats with different infarct size after beta-adrenergic blockade and ACE-inhibition.

We tested whether ACE-inhibition with ramipril (A), beta-adrenergic blockade with metoprolol (beta) or combined treatment (beta A) for 6 weeks after inducing myocardial infarction in rats by left coronary artery ligation modifies contractile function of hypertrophied papillary muscle from left ventricles with different infarct size (IS) compared to a placebo group (P). At IS<40% of left ventricle, contraction and relaxation were less impaired than at IS>40% compared to sham operated rats (SO). Isometrically developed peak force and calcium sensitivity of myofilaments, measured in skinned fibres, were significantly higher in beta. Treatment with ramipril or metoprolol improved contraction rate and force development, respectively, mainly at IS<40%, but deteriorated relaxation rate. ACE-inhibition and beta-adrenergic blockade had no significant improving effect on the relaxation rate and further characteristics of the contractile function at IS>40%, although combined treatment reduced the infarct size and ramipril treatment suppressed the development of hypertrophy. Post-extrastimulatory potentiation was increased in beta and beta A at IS>40%. Post-rest potentiations were influenced hardly at IS<40% and were significantly smaller in A at IS>40%. The twitch-to-twitch decay of the potentiations was faster at IS>40%. Increase in the degree of post-extrastimulatory potentiation, steeper twitch-dependent decay of the potentiations and loss of rest-dependent potentiation at IS>40% indicate relatively increased trans-sarcolemmal Ca2+ transports via Ca2+ channels and Na+/Ca2+ exchange, partly modified by ramipril and metoprolol. The results demonstrate that ACE-inhibition and beta-adrenergic blockade induce a dissociation between trophic effects and phenotypic effects on contractile function after chronic infarction.

Adrenergic beta-Antagonists↗

PubMed1995

Analysis of alternans in late potentials. Correlations between epicardial and body surface recordings.

The methodical performance of the signal-averaged electrocardiogram is strongly influenced by the beat-to-beat reproducibility of late potentials (LPs). Especially at higher heart rates, epicardial recordings from infarct regions show progressive beat-to-beat prolongations with alternating conduction block. To analyze the influence of beat-to-beat-alternans of LPs on the signal-averaging process, epicardial and body surface recordings were studied at different heart rates and extrastimulation. Epicardial and body surface recordings were obtained from dogs with 4-day postligation of the left anterior descending coronary artery (Harris model). Body surface potentials were averaged in different modes to a final noise level of 0.3 microV (rms) and digitally bandpass filtered (40-250 Hz). Modulation of the heart rate was performed by atrial or His-bundle pacing and by atrial premature extrastimulation. Pacing up to heart rates close to 180 beats/min produced no significant changes in the duration of LPs in epicardial and averaged body surface recordings; however, at higher pacing rates, considerable prolongation of LPs with different patterns in the epicardial leads was observed. In these cases, averaging of all beats revealed only a slight prolongation of LPs, as seen from the body surface. Selective averaging of beats with prolonged epicardial LPs showed the prolongation or absence of LPs, as seen in the epicardial recordings. Similar observations were made using an atrial extrastimulation technique, whereby the average of the premature beats was compared to the average of all normal sinus beats. Selective beat averaging of body surface potentials can unmask the prolongation of LPs due to atrial pacing or extrastimulation, as seen in recordings from the infarcted epicardium. The evidence of this modulation of LPs may improve the positive predictive value of the signal-averaged electrocardiogram.

Action Potentials↗

PubMed1991

A new approach towards defibrillation electrodes: highly conductive isotropic carbon fibers.

A new carbon fiber material was studied for its potential benefit in defibrillation electrodes. Miniaturization of the fiber production can result in small strands with extremely large surface areas. Two carbon fiber patches and a single carbon fiber bundle were used for the purposes of this study, and the results were compared to those obtained with conventional titanium/mesh patch electrodes. Tests performed in a saline filled tank revealed considerably lower resistances through the carbon material when compared to standard mesh electrodes. There was also a higher peak current flow with lower voltage. The carbon fibers exhibited lower impedance for defibrillation and this may be related to low polarization known to occur with carbon materials. This new carbon material may prove to be useful and further research is required.

Carbon↗

PubMed1990

[A new mechanical sensor for activity controlled and body position dependent frequency adaptive pacemaker stimulation].

In the past, the most important feature in the development of rate-responsive pacemaker systems was ensuring an adequate rate response to physical exercise. But there are other variables that modulate the rate of the healthy heart; examples include postural changes in heart rate in order to prevent orthostatic reactions, and the nightly decrease in intrinsic pacemaker rate. Therefore, we developed a sensor that could distinguish, not only rest and activity, but also discriminate between a supine and an upright position. This sensor is a multicontact tilt switch, which contains a small mercury ball. By measuring the number of openings and closures within the sensor as the ball touches the numerous sensor contacts it is possible to discriminate between different levels of exercise; the contact pins are circled around the base plate. There is an almost linear increase in the number of changes per time with increasing exercise. Besides measuring body activity from the number of contact changes per time, it is also possible to determine the body's posture from the count and positioning of the closed contacts within the casing. Based upon the results of 12 volunteers and nine pacemaker patients, a new algorithm is being prepared which enables the pacemaker to decrease stimulation rate in the supine position, to increase it in the upright position, and to correlate pacing rate with the increase in physical exercise. There is a good correlation between number of contact changes and the intrinsic heart rate (r = 0.87).

Adult↗

PubMed1989

The basis for activity controlled rate variable cardiac pacemakers: an analysis of mechanical forces on the human body induced by exercise and environment.

We conducted tests on six healthy volunteers and six pacemaker patients. With the aid of three straight line frequency acceleration pickups attached to the body, the mechanical signals were recorded on the three axes during different activities. Along with standardized exercise on bicycle and treadmill ergometers, we tested the influence of household activities and interference influences. The results were analyzed in terms of the amplitude and frequency content of the signals. For walking activities, we found a signal amplitude increasing in a largely linear fashion with the walking speed, the signal amplitudes being approximately twice as high on the vertical axis as on the other two axes. Exercise on the bicycle ergometer produced mechanical signals of clearly lower amplitude than comparable walking activities. The Fast-Fourier analysis showed amplitude peaks in the low frequency range of 1 to 4 Hz for all forms of physiological exercise, while interference influences showed amplitude peaks mainly in the range above 8 Hz. The use of a straight line-frequency acceleration pickup and a corresponding low pass filter might be a way of reducing the effect of unphysiological interference influences on an activity controlled pacemaker system. A sensor measuring on the horizontal axis appears to be the most favorable compromise for the various types of exercise. However, due to the considerable difference in signal amplitude for different types of exercise of the same intensity, an activity controlled pacemaker system cannot entirely meet metabolic conditions and requirements.

Activities of Daily Living↗

PubMed1989

[Principle of the activity-controlled rate-adaptive cardiac pacemaker: analysis of stress and environment-induced mechanical effects on the human body].

Rate-adaptive pacemakers are increasingly becoming part of clinical routine, the most widespread systems being activity-controlled. In order to shed more light on the foundations of mechanical forces which can possibly be utilized for controlling rate-adaptive systems, we conducted tests on six healthy volunteers and six pacemaker patients. With the aid of three orthogonal wide-band linear acceleration pick-ups attached to the body, the mechanical signals were recorded from the three axes during different activities. Along with standardized exercise on bicycle and treadmill ergometers, we tested the influence of household activities and interference influences. The results were analyzed in terms of the amplitude and frequency content of the signals. For walking activities we found a signal amplitude increasing in largely linear fashion with the walking speed, the signal amplitudes being approximately twice as high on the vertical axis as on the other two axes. Exercise on the bicycle ergometer produced mechanical signals of clearly lower amplitude than comparable walking activities. The Fast-Fourier analysis showed amplitude peaks in the low frequency range of 1 to 4 Hz for all forms of physiological exercise, while interference influences showed amplitude peaks mainly in the range above 8 Hz. The use of an acceleration pickup and a corresponding low pass filter might be a way of reducing the effect of nonphysiological interference influences on an activity-controlled pacemaker system. A sensor measuring in the horizontal axis appears to be the most favorable compromise for the various types of exercise. However, due to the considerable difference in signal amplitude for different types of exercise of the same intensity, an activity-controlled pacemaker system cannot entirely meet metabolic conditions and requirements.

Adult↗

PubMed1988

A new rate-modulated pacemaker system optimized by combination of two sensors.

A new rate-modulated pacemaker system optimized by combination of two sensors is described. The parameter body activity and central venous blood temperature control the pacemaker rate. The specific characteristic of each parameter determines its role within the algorithm. While the motion sensor yields a fast reaction following the onset or a change of stress intensity, central venous blood temperature corresponds better to body metabolism. An indication of increased exercise from the motion sensor results in an accordingly rapid increase in the pacing rate. Unless this increased exercise is confirmed by an increase in central venous blood temperature within 2 or 3 minutes, the new motion level will be assumed to be the new baseline motion value and the pace rate will return to a basic pacing rate. Prolonged inappropriate responses are therefore avoided. Longer lasting exercise, fever and nonphysiological signals are recognized and handled safely. Exercise tests with five volunteers under various conditions showed pacing rate behavior that was close to normal.

Adult↗

PubMed1988

Which patient is most likely to benefit from a rate responsive pacemaker?

In order to provide information about indications for rate responsive pacing, we examined the exercise capacity of a typical collective of pacemaker patients. One hundred seven patients participated in the study, 50/107 (46.8%) suffered from sick sinus syndrome, 37/107 (34.6%) showed complete AV block, 12/107 (11.2%) had bradyarrhythmia and 8/107 (7.4%) had other diseases. All patients underwent treadmill exercise with increasing workloads up to the individual's maximum workload. We monitored heart rate, respiratory rate, workload, the subjective perception of stress according to the Borg scale, and the reason for the termination of exercise. Calculation of oxygen uptake was done according to an equation given by Givoni. During the tests, all implanted pacemakers have been programmed to VVI 70 mode. We found that all pacemaker patients showed a reduction of their exercise capacity compared to the age-related normal values. Particularly in patients with AV block or bradyarrhythmia, the maximum achievable workload often did not even reach levels of everyday activities such as going upstairs; patients with sick sinus syndrome showed slightly better exercise capability, probably due to the higher increase of average heart rate. Despite objective differences of maximum workload, all patients had the same subjective perception at the end of the tests; the course of respiratory rate indicated that all persons finished the tests in the range of individual maximum exercise capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Bradycardia↗

PubMed1988

A new mechanical sensor for detecting body activity and posture, suitable for rate responsive pacing.

In the past, thought about rate responsive pacing mainly focused on rate increase with exercise but did not consider that a rate increase with postural changes also is mandatory in order to prevent orthostatic reactions. A nightly decrease in pacemaker rate when the body is at rest and in a supine position is a further advantage for the patient's sleep and recovery. Therefore, we developed a sensor that could detect not only rest and body activity but also discriminate between a supine and an upright position. This sensor is a multicontact tilt switch containing a small mercury ball, as shown in the left panel of the figure below. The principle of discrimination between rest and low and high body activity is realized by the movement of the mercury ball resulting from body motion, which causes openings and closures within the sensor as the ball touches the numerous sensor contacts. In the upright position, a distinct number of contacts at the bottom of the tilt switch are closed. In the supine position, there is no closure of the bottom contacts and a postural discrimination can be achieved. We studied 12 volunteers and 10 pacemaker patients with this new device both at rest and during physical exercise. The right panel of the figure illustrates that the contacts per second correlate to the increase of physical exercise, such as walking on the treadmill. Further studies with an external pacemaker containing a small sensor suitable to fit into the pacemaker are in preparation.

Adult↗

PubMed1988

[Behavior of central venous blood temperature in short duration and repeated stress--possibilities for temperature controlled frequency-adapted pacemaker stimulation].

Although an exercise-induced increase in blood temperature has been well-known for some time, there was still some doubt whether the change in central venous blood temperature with short-lasting and repetitive physical exercise can be measured and utilized by a temperature controlled pacing system. We studied the central venous blood temperature with short-lasting and repetitive exercise in ten healthy young volunteers and in ten pacemaker patients. The blood temperature was measured intracardially while they walked upstairs. A height of 20 m was covered within 100 +/- 5 s. An oxygen uptake of 27 ml/min/kg was calculated for this level of exercise. After walking upstairs once, the volunteers had an increase in central venous blood temperature of 0.3 degrees C and the pacemaker patients of 0.37 degrees C. After walking upstairs three times, the volunteers had an overall rise in blood temperature of 0.67 degrees C and the pacemaker patients of 0.86 degrees C. Thus, the central venous blood temperature shows a pronounced, measurable increase with short-lasting exercise as well. However, the rises in blood temperature accumulate with repetitive exercise, as the duration of exercise (100 s) when walking upstairs once is not sufficient for a new level of temperature to be reached according to the level of exercise. Thus, a temperature controlled pacing system should take these complex changes into consideration.

Adult↗