Cardiac Pacemaker Regulated by Respiratory Rate and Blood Temperature

A new method using respiratory rate and temperature as the guides for optimal pacing is proposed. A pacemaker was fabricated which senses these two parameters simultaneously. The pacemaker functions by calculating the cardiac rate, which would be derived from the respiratory rate and the blood temperature. The higher of the two rates is adopted as the cardiac pacing rate, i.e., at which stimuli will be delivered. The operation was tested in a mongrel dog with complete atrioventricular block. After the induction of anesthesia, a thermistor temperature probe was inserted into right atrium and a respiratory rate sensor was attached around the chest. After administration of a pyrogenic drug, both respiratory rate and blood temperature increased. The pacing rate was increased from 178 beats/minute(bpm) at 36.4 degrees C, blood temperature, and 26.5 acts/minute(apm), respiratory rate, to 233 bpm at 40.1 degrees C and 40.0 apm. Cardiac output was increased from 2.15 liters/minute(l/pm) at the beginning to 2.50 l/pm at maximum. The transition of the guide from respiratory rate to temperature was observed at about 38 degrees C.     

Rate Modulation by Arm Movements of the Respiratory Dependent Rate Responsive Pacemaker

The rate response to arm movements of the respiratory dependent rate responsive pacemaker (RDP3, Biotec) was assessed in four patients implanted with this pacemaker. The pacemaker was implanted in the left prepectoral region and the auxiliary impedance measuring electrode positioned subcutaneously over the right second intercostal space with its tip lateral to the mid-clavicular line. The lower rate of the pacemaker was programmed to 75 bpm. While holding the breath, swinging arm movements (30 times) resulted in rate acceleration. The peak rate was faster when the arm on the side of the auxiliary electrode was swung (mean ± SEM, 117 ±8 compared to 130 ± 5 bpm, P < 0.5). The mean rate response of the subjects to brie/ treadmill exercise (Bruce stage 1) performed with both hands holding the support rails, swinging the right arm only, swinging left arm only and swinging both arms were 108, 140, 135 and 128 bpm respectively. Impedance measurement confirmed the significant influence of arm movements on thoracic "impedance" changes, which was mainly caused by electrode motion artifacts affecting the two electrode measuring system. This effect was dependent on the relative positions of the impedance measuring electrodes (i.e., between the pacemaker casing the auxiliary lead). Subsequently the auxiliary lead of the respiratory pacemaker (MB-1, and Biorate) was implanted in the lower part of the chest on the right sternal edge in another patient. Rate acceleration was only observed when the arm on the side of the pacemaker was swung. As arm movements often accompany physical activities, pacing rate can be affected and should be considered when programming this pacemaker.     

Increasing Cardiac Rate by Measurement of Right Ventricular Temperature

Un stimulateur qui augments sa Fréquence en fonction de l'exercice permet au patient d'améliorer son état de bien-être. Les capteurs pourraient utiliser la fréquence auriculaire, l'espace QT, le pH, la saturation d'oxygène du sang veineux, la fréquence ventilatoire, le débit cardiaque, les mouvements du corps et la température sanguine. Afin de déterminer l'éfficacité de la reconnaissance de l'exercice par utilisant la température du sang du ventricule droit, un stimulateur expérimental a été développé et évalué chez le chien. Un algorithme a été incorporé dans un stimulateur VVI comportant un microprocesseur, qui pourrait détecter l'exercice et le repos à partir de la température sanguine Deux fréquences de stimulation étaient done possibles pour améliorer le débit cardiaque. Des etudes sont en cours peur démontrer la fisabilité d'un tel systéme chez l'homme.     

Follow-Up of a Respiratory Rate Modulated Pacemaker

The efficacy of 27 respiration sensitive rate modulated pacemakers (Biorate RDP-3 Biotec) implanted in the left pectoral area was evaluated every 3 months during a mean follow-up period of 29 months (range 10-50 months). Rate modulation function was unchanged other than for three patients in whom the auxiliary leads became displaced. Two implants lost ventricular sensing in this nonprogrammable model. In all but the three patients, Holter monitoring demonstrated pacing rate variation corresponding to daily activity. Stress test duration increased from 8.2 +/- 1.5 minutes (in fixed rate VVI rate) to 12.83 +/- 2.0 minutes (in the VVIR mode) (P less than 0.05). Right arm movement increased the pacing rate by 5 +/- 3 beats/min (NS), while the left arm movement increase was 30 +/- 5 beats/min (P less than 0.05). Mental, arithmetic, and nifedipine tests did not change the rate modulated pacing rate. The system responded to a change in respiratory rate by an increase in stimulation rate. A satisfactory response in sensitivity and velocity was present only with medium-high workloads. Interference with rate modulation occurred with movement of the arm ipsilateral to the implanted pulse generator.     

Respiratory Rate as a Determinant of Optimal Pacing Rate

Des essais ont été faits dans ľutilisation des paramètres bialogiques pour déterminer la fréquence optimale de stimulation cardiaque. Dans cette étude, le rapport entre fréquence respiratoire et fréquence cordiaque a étéétabli chez 67 patients au cours de ľexercice. Ensuite, un système de stimulation cardiaque qui repondrait àľactivation radiotélémétrique a été posé chez onze patients. Dans deux cos un système automatique a été implanté avec succès. A present, les résultats de cette stimulation pilotée par la fréquence respiratoire sont satisfaisants.
Efforts have been made to utilize biologic parameters for determining optimal cardiac pacing rates. In this study of 67 patients, a significant relationship between heart rate and respiratory rate was observed during dynamic exercise. A system using a radiofrequency activator to modify pacing rate is described. Eleven patients have received VVI pacemakers with a similar implanted radioreceiver coil. In two patients the fully automatic system has been successfully implanted. The experience with respiratory rate as a determinant of pacing rate is encouraging.     

Circumvention of Maximum Tracking Limitations with a Rate Modulated Dual Chamber Pacemaker

A patient having high grade AV block with intact sinus node function is presented in whom DDDR pacing provided the benefit of preventing 2:1 pacemaker block in response to exercise-induced sinus tachycardia. In paired treadmill tests with the patient blinded as to pacing mode, she was able to exercise longer (7.5 vs 6.6 METS) when programmed in DDDR than in DDDO. This is attributable to circumvention of 2:1 pacemaker block which had resulted in abrupt onset of fatigue and SOB (shortness of breath) when the sinus rate exceeded the maximum tracking rate of 130/min. Outpatient ambulatory electrocardiographic monitoring confirmed this phenomenon during relatively strenuous activity. The theoretic advantages of dual chamber rate modulated pacing compared to the DDDO and VVIR modes are discussed.     

Follow-Up of a Minute Ventilation Rate Adaptive Pacemaker

Although rate adaptive pacemakers are now frequently prescribed, there is limited information regarding long-term follow-up of patients with a pacemaker capable of rate adaptation. We have examined our patients in whom a pacemaker capable of rate adaptation via a sensor that determines minute ventilation has been implanted. After following a group of 42 patients for a mean of 13.2 months we have found this to be a reliable rate adaptive pacing system. The sensor was reliable long term, the system is easy to program, and sensor settings were changed infrequently.     

Single Versus Double Chamber Rate Responsive Cardiac Pacing: Comparison by Cardiopulmonary Noninvasive Exercise Testing

A new double chamber rate responsive cardiac pacemaker (DDDMR) bas been implanted in seven patients (four males and three females) with a mean age of 62 years. Indication for pacemaker treatment was complete AV block in two patients, complete AV block associated to sinus node disease in three patients and sinus node disease alone in two patients. Six patients underwent two maximal stress tests on a cycloergometer performed twice randomly starting with WIMR or DDDMR. Basic work load of 50 watts was increased by steps of 25 watts every 2 minutes. Heart rate, respiratory frequency, blood pressure, exercise duration, maximal charge developed, oxygen consumption, rate pressure product, efficiency and Borg scale were compared. Our results show a general trend but no significant differences between ail the measured parameters except for efficiency which was significantly higher with DDDMR. These results prove a slight improvement of cardiopulmonary performance in DDDMR pacing compared to WIMR and also confirm the importance of atrial contribution to cardiac output on exercise.     

Cardiac Rehabilitation in Patients with Rate Responsive Pacemakers

This study investigated the suitability of our oxygen pulse reserve (OPR) method for tailoring parameters of rate responsive pacemakers and planning aerobic rehabilitation programs. We selected 11 patients, NYHA Classes I-III (7 males and 4 females; mean age 60 years, range 18–83), with rate responsive pacemakers implanted for high degree AV block and chronotropic incompetence. Five pacemakers had activity sensors, 4 had temperature sensors, and 2 had dual sensors. All patients underwent a cardiopulmonary stress test (CPX). We determined anaerobic threshold time (ATT), VO₂/AT, total exercise time (TET), VO₂ Max, and VO₂AT/VO₂ Max. OPR (mL-O₂/beat) was calculated for each patient using the formula OPR = (VO₂Max - VO₂ resting)/(HR Max - HR resting). During CPX, this slope was used as the rate response tailoring guideline by comparing the mL-O₂/beat equation and the pacing rate. Rate response settings were modified until the optimal relationship between theoretical and paced rate was obtained. The work protocol yielded rate response settings capable of providing pacing rates within ± 10 beats of the theoretical values. Data relating to theoretical and measured rates have been analyzed statistically. Patients underwent an aerobic rehabilitation program that followed the American College of Sports Medicine guidelines. Pacing rate at the anaerobic threshold was considered the border for an aerobic workload. After 2–7 months, all patients showed an evident improvement in ATT (92%), VO₂/AT(48%), TET(49%), VO-,Max (23%), and VO₂ AT/VO₂ (21%). Particularly, two patients improved from Weber Class C to A, and three improved from C to B. At each CPX step, the mean values of pacing rate and theoretical rate almost overlap, and the relevant coefficients suggest an excellent correlation (P < 0.001). Our OPR method for tailoring rate response provides the basis for an effective rehabilitation program with functional advantages for patients.     

A Fully Automated Algorithm for the Determination of Respiratory Rate from the Photoplethysmogram

Objective. To determine if an automatic algorithm using wavelet analysis techniques can be used to reliably determine respiratory rate from the photoplethysmogram (PPG). Methods. Photoplethysmograms were obtained from 12 spontaneously breathing healthy adult volunteers. Three related wavelet transforms were automatically polled to obtain a measure of respiratory rate. This was compared with a secondary timing signal obtained by asking the volunteers to actuate a small push button switch, held in their right hand, in synchronisation with their respiration. In addition, individual breaths were resolved using the wavelet-method to identify the source of any discrepancies. Results. Volunteer respiratory rates varied from 6.56 to 18.89 breaths per minute. Through training of the algorithm it was possible to determine a respiratory rate for all 12 traces acquired during the study. The maximum error between the PPG derived rates and the manually determined rate was found to be 7.9%. Conclusion. Our technique allows the accurate measurement of respiratory rate from the photoplethysmogram, and leads the way for developing a simple non-invasive combined respiration and saturation monitor. Paul A. Leonard, J. Graham Douglas, Neil R. Grubb, David Clifton, Paul S. Addison, James N. Watson. A fully automated algorithm for the determination of respiratory rate from the photoplethysmogram     

Automatic Sensor Adjustment in a Rate Modulated Pacemaker

A new feature (AutoSlope) has been introduced that can automatically adjust the sensor slope based on the chronic activity level of the patient. The algorithm adjusts the slope once per week so that 99% of the sensor response is maintained between the base rate and 23% of the difference between the programmed Base Rate and the Max Sensor Rate. Offsets are available for fine titration of sensor response in individual patients. The AutoSlope feature was evaluated in 93 patients with DDDR pacemakers (Trilogy DR+, Pacesetter). Patients were seen at 1, 3, and 6 months for a total of 178 evaluations. At each evaluation, the AutoSlope value was recorded. Patients then performed a brisk walk at sensor values equivalent to the AutoSlope value. Desired sensor rate was compared to the rate achieved by AutoSlope for the exercise period. Long-term sensor performance was evaluated by analyzing the sensor histogram. AutoSlope provided the desired sensor rate in most patients. Use of AutoSlope offsets allows fine titration of rate modulation in individual patients. Ongoing changes in sensor performance provided by AutoSlope allow patients to achieve a desired sensor rate from one evaluation to another without changes in permanent programmed settings. Programming a low maximum sensor rate may limit sensor response in some patients.     

Initial Experience with a New Single Chamber, Dual Sensor Rate Responsive Pacemaker

In August 1991, a new single chamber pacemaker became available that utilizes information from two sensors, activity and stimulus-to-T wave (QT) interval. We are reporting on the first 90 implants in 21 centers. T wave sensing was adequate at implantation in 88/90 patients, with a safety margin of > 100% in 86/90, Activity sensing was adequate in all patients. The contribution of each sensor fsensor blending) is programmable for each patient. Of 75 patients assessed at 1 month after implant, three have been programmed to "Activity-Only" mode, and 72 to dual sensor mode. Of these, 18 have been programmed to "QT < Activity," 48 to "QT = Activity," and 6 to "QT > Activity." Forty-five patients underwent exercise testing in dual sensor mode and a subgroup of 15 also underwent exercise testing in Activity-Only mode. The dual sensor mode produced a more gradual increase in pacing rate. Sensor Cross Checking^tmsatisfactorily prevented a sustained high pacing rate in tests of false-positive activity sensing (tapping, vibrating pacemaker, or static pressure). The maximum pacing rate on walking downstairs (94.2 ± 7.2 ppm) was similar to that produced by walking upstairs (91.6 ± 5.9 ppm). We conclude that initial assessment of this dual sensor, single chamber, rate responsive pacemaker confirms that the algorithm for combining data from two sensors functions satisfactorily. Dual sensor rate responsive pacing may offer significant advantages over single sensor devices, and further studies of this novel device are indicated.     

Measurement Of Respiratory Rate From the Photoplethysmogram In Chest Clinic Patients

OBJECTIVE: We studied the application of our algorithm for the robust extraction of respiratory information from the pulse oximeter signal acquired from a selection of patients attending the chest clinic. METHODS: Photoplethysmograms were obtained from 16 individuals: 13 patients with various conditions in the respiratory ward and three healthy subjects. Wavelet transforms were generated from which respiratory information was extracted to obtain a measure of respiratory rate. This measured rate was compared with the respiratory rate determined by one of a variety of other means (a digital end tidal CO(2) signal, the output from a non-invasive ventilation device, or a switch actuated by the patient or observer.) RESULTS: Respiratory rates varied from 6.2 to 35.8 breaths per minute (bpm). The oximeter rate determined through our method matched the marker rate obtained for all patients to within 1 bpm. CONCLUSION: The technique allows the measurement of respiratory rate directly from the photoplethysmogram of a pulse oximeter, and leads the way for development of a simple non-invasive combined respiration and saturation monitor useful for patients with all forms of breathlessness.     

Oxygen Pressure as Biosensor for Rate Adaptive Cardiac Pacing

A new carbon based oxygen sensor for rate adaptive cardiac pacing has been developed. It measures oxygen partial pressure In mixed venous blood. The system was implanted in six sheep with a mean follow-up time of 261 days after implant. The sensor reacted in a physiological manner when the animals were at rest as well as during exercise. Long-term sensor stability and sensitivity were satisfactory, and we found excellent correlation with spontaneous heart rate variations and with oxygen saturation measurements. The sensor shows great promise although our experience is still limited and further development on the concept is on-going.     

Overnight Heart Rate and Cardiac Function in Patients with Dual Chamber Pacemakers

Animal data indicate that chronic, overnight pacing at normal evening heart rates impairs cardiac function. We examined the relationship of pacing rate and cardiac function in nine patients with dual-chamber pacemakers. We investigated two, 3-week pacing regimens (80 and 50 ppm: DDD mode) in a cross-over design. Doppler echocardiograms were performed at 1700 hours (PM) and 0600 hours (AM) at the end of each regimen. Ventricular function and preload decreased overnight (PM vs AM) with both pacing regimens. Compared to the morning values, the ratio of preejection to ejection time (PEP/ET) rose (0.43 vs 0.46), while the mean velocity of circumferential fiber shortening (V_cf) fell (1.16 cm/s vs 1.11 cm/s). Stroke volume (SV) (61 mL vs 53 mL) and ejection fraction (EF) also fell (0.56 vs 0.53) in the morning, End-diastolic volume (EDV) (94 mL vs 88 mL) decreased in the morning, as did the ratio of passive to active filling (E/A) (1.06 vs 0.96). Iscvolumic relaxation time(91 msvs 101 ms) increased overnight at both pacing rates. Systolic function decreased at 80 ppm relative to 50 ppm at both times of day. SV fell (54 mL vs 61 mL), while both EDV (92 mL vs 90 mL) and end-systolic volume (ESV) increased (43 mL vs 40 mL). Contractility measured by V_cf(1.09 cm/s vs 1.18 cm/s) and PEP/ET (0.49 vs 0.41) was reduced at 80 ppm. The heart needs to rest at night by slowing its rate of contraction. Pacing at 80 ppm impairs systolic and diastolic ventricular function compared to 50 ppm. Longer term consequences of ostensibly physiological pacing rates merit inquiry, particularly in those with preexisting cardiac dysfunction.     

Clinical Evaluation of a Dual Sensor, Rate Responsive Pacemaker

Dual sensor pacemakers should respond more appropriately during differing exercise modes than a single sensor device. The Topaz™ models 515 (QT and activity count [ACT] sensing) pacemaker shows appropriate rate response during treadmill exercise testing. We postulated that adjustments to relative sensor contribution should allow fine tuning of the onset of rate response. Eleven patients with this pacemaker were studied. Three standard exercise tests were performed with adjustment of sensor blending and activity threshold between each one. We also assessed the response to isometric exercise and a false positive activity signal. Results : Times to 100 ppm (3.7 ± 1.3, 4.4 ± 2.0, 5.3 ±1.5 mins), times to peak rate (6.1 ± 1.6, 5.6 ± 1.4, 6.5 ± 1.3 mins) and accelerations to peak (9.0 ± 2.4, 9.2 ± 5.3, 7.7 ± 2.8 ppm/min) were measured in all three different sensor settings (QT = ACT, QT 相似文献   

Diagnosis of Early Cardiac Transplant Rejection by Fall in Evoked T Wave Amplitude Measured Using an Externalized QT Driven Rate Responsive Pacemaker

Reliable diagnosis of cardiac ailograft rejection is at present only possible using endomyocardial biopsy. We have serially measured epicardial evoked T wave amplitude during ventricular pacing with an externalized QT driven rate responsive pacemaker telemetered to a TP2 analyzer in 13 patients (12 males) followed for 19 (14–26) days after transplantation. A total of 228 records were analyzed. Rejection was defined on endom-yocardial biopsy. On 17 of the 31 occasions on which biopsy was performed during the study, specimens showed significant (moderate) rejection. In 11 patients the initial biopsy proven rejection episode was associated with a significant fall in the evoked T wave amplitude from 1.3 (0.7–2.3) mV to 0.6 (0.5–1.8) mV (P < 0.005), which began 2 (1–4) days earlier. One patient with uncontrolled diabetes mellitus had no change in evoked T wave amplitude during rejection. The evoked T wave amplitude did not fall in the absence of histologic rejection. These results suggest a noninvasive method for detecting cardiac rejection, which appears both sensitive (92%) and specific (100%) in the first rejection episodes.     

Relationship Between Heart Rate and Minute Ventilation, Tidal Volume and Respiratory Rate During Brief and Low Level Exercise

The correlation between heart rate (HR) and three respiratory parameters, minute ventilation (VE), tidal volume (Vt), and respiratory rate (RR), were studied. Four healthy subjects performed four exercise tests duration 30 seconds at 50, 100, 150, or 200 W), in random order. Cardio-respiratory parameters were recorded respiratory cycle by respiratory cycle. The results of these low level exercise tests showed that oxygen consumption (VO₂) was strongly correlated with VE (r = 0.91 ± 0.10; P < 0.01) (except in one test) and Vt (r =0.91 ± 0.07; P < 0.001) (except in one test). There was no significant correlation between VO² and RR. At exercise onset HR, VE, and Vt were modified in a matter of a few heart beats while RR varied depending on the subject and the level of exercise. During exercise average HR, VE, and Vt were significantly higher than at rest in most cases; but RR was not significantly changed by exercise. The correlations between HR and VE, Vt and RR varied from one individual to another. Nevertheless, the correlation coefficients were positive for VE and Vt, while they were negative for RR. Sensing respiratory rate thus appears to be insufficient for responsive pacing of exercise onset, but sensing respiratory volumes (Vt, VE) should give satisfactory results.     

Increased Tidal Volume Variability in Children is a Better Marker of Opioid-Induced Respiratory Depression than Decreased Respiratory Rate

OBJECTIVE: During opioid administration, decreasing respiratory rate is typically used as a predictor of respiratory depression. Prior to opioid-induced apnea, progressively irregular breathing patterns have been noticed. We hypothesize that opioid administration to children will increase tidal volume variability (TV(var)) and that this will be a better predictor of respiratory depression than a decrease in respiratory rate. METHODS: We recruited 32 children aged 2-8 years scheduled to undergo surgery. During spontaneous ventilation, flow rates and respiratory rates were continuously recorded, while remifentanil was infused at stepwise increasing doses each lasting 10 min. The infusion was continued until the patient showed signs of respiratory depression. Flow data from each dose was used to calculate tidal volumes, from which TV(var) was calculated. The respiratory rate and TV(var) during the last (D(last)), second to last (D-2), and third to last (D-3), administered doses were compared to those during baseline (fourth to last dose). We chose a threshold of TV(var) increase and compared it to a decrease in respiratory rate below 10 breaths per min as predictors of respiratory depression. RESULTS: Compared to baseline, the TV(var) increased by 336% and 668% during D(-2) and D(last), respectively, whereas respiratory rate decreased by 14.3%, 31.7%, and 55.5% during D(-3), D(-2), and D(last), respectively. A threshold increase in TV(var) of 150% over baseline correctly predicted respiratory depression in 41% of patients, compared to a drop in respiratory rate correctly predicting 22% of patients. CONCLUSIONS: TV(var) increases as children approach opioid-induced respiratory depression. This is a more useful predictor of respiratory depression than a fall in respiratory rate because the TV(var) increase is 10 times the drop in respiratory rate. A TV(var) increase also correctly predicts respiratory depression twice as often as decreased respiratory rate and is independent of age-related alterations in physiologic respiratory rates.     

Rate Responsive Cardiac Pacing Using a Minute Ventilation Sensor

A minute ventilation sensing rate responsive pacemaker was implanted in 15 patients (8 males and 7 females)with bradycardia. The mean age was 72.8 ± 8.7 years. The single chamber system measures transthoracic impedance between the tip electrode of a standard bipolar lead and the pulse generator case. In the adaptive mode the pulse generator calculates a rate responsive factor or slope during maximal exercise but /unctions as in the VVI mode. The patients exercised maximally on an upright cycle ergometer with the pacemaker programmed to VVI mode, adaptive mode, and rate responsive mode. Exercise and gas exchange data were collected continuously and analyzed using an automated breath-by-breath system. The slope, heort rate, and ventilation were measured every 20 seconds. Heart rate in pacemaker dependent patients correlated well to minute ventilation (correlation coefficient ranging from 0.72–0.95, P < 0.0001). This study demonstrates that minute ventilation is a good metabolic sensor in rate responsive pacing.