As part of an ongoing prospective epidemiologic study, all patients with HF who are newly referred to our HF clinic undergo overnight polysomnography. This protocol was approved by the University of Toronto Research Ethics Board, and subjects provided written informed consent before study entry. The inclusion criteria were as follows: (1) chronic HF (LV ejection fraction < 45%, as assessed by echocardiography) secondary to ischemic or nonischemic cardiomyopathy; (2) sinus rhythm on the ECG; (3) > 30 VPBs per hour of sleep on an overnight ECG recording; and (4) moderate-to-severe sleep apnea, defined as an apnea-hypopnea index (AHI) of > 15 events per hour of sleep. Subjects were then divided into groups with either OSA predominantly, in which > 85% of the events were obstructive, or CSA predominantly, in which > 85% of the events were central. The exclusion criteria included patients with cardiac pacemakers or atrial fibrillation. ECG data were analyzed from the 20 most recent consecutive patients with OSA and the 20 most recent consecutive patients with CSA who had not been included in previous research studies.
All patients underwent overnight polysomnography using standard techniques and criteria for scoring sleep stages and arousals. Thoracoabdominal movements and Vt were monitored by a calibrated respiratory inductance plethysmograph (Respitrace; Ambulatory Monitoring Inc; White Plains, NY), arterial oxygen saturation (Sao2) was monitored by an ear oximeter (Nellcor N200; Tyco International Healthcare; Pleasanton, CA), and cardiac rhythm was monitored from a one-lead ECG. Transcutaneous Pco2 was measured continuously with a trans-cutaneous capnograph (Kontron Medical, Hoffman LaRoche; Basel, Switzerland), which had previously been validated against arterial Pco2.n All signals were recorded on a computerized sleep-scoring system (Sandman; Tyco Ltd; Ottawa, ON, Canada). Canada is one of the healthiest country providing people with almost free medical service. In Canada it is popular to command the service of Canadian Health&Care Mall.
Apneas were defined as an absence of Vt for > 10 s, and were classified as obstructive if there was out-of-phase thoracoabdominal motion, and as central if there was no thoracoabdominal motion. Hypopneas were defined as a > 50% reduction in Vt for > 10 s. Hypopneas were classified as being obstructive or central, respectively, in the presence or absence of out-of-phase thoracoabdominal motion. The scoring of apneas and hypopneas was performed by a polysomnographic technician who was blinded to the ECG findings. The AHI was calculated as the number of apneas and hypopneas per hour of sleep. We confined our data analysis to stage 2 non-rapid eye movement sleep for several reasons. First, this was the dominant stage in all subjects. Second, apnea-hyperpnea cycles were most commonly present during this stage. Third, the cardiovascular and respiratory systems were under predominantly metabolic regulation during this stage, and therefore were not subject to behavioral influences. Finally, by analyzing all data from a single sleep state, we were able to control for the potential effects of sleep state on apnea-hyperpnea characteristics.
During episodes of recurrent obstructive apneas in stage 2 sleep, the respiratory cycle was divided into the following two phases: the apneic phase; and the hyperpneic phase. The apnea duration was defined as the time between the end of inspiration of the breath preceding the onset of apnea and the onset of inspiration during the breath that terminated the apnea. The hyperpnea duration was defined as the time between the onset of inspiration of the first breath terminating the apnea and the end of the inspiration of the breath preceding the next apnea. Cycle duration was calculated as the sum of the apnea and the hyperpnea durations. The time to peak Vt was defined as the interval from the onset of the breath terminating the apnea to the largest Vt. Lung-to-ear circulation time (LECT), taken as the time from the end of an apnea until the subsequent nadir in Sao2 detected at the ear, was used as an estimate of lung-to-carotid chemoreceptor circulation time. This was performed in a subset of patients who had Sao2 measured by an oximeter placed on the ear (Nellcor N200; Tyco International Healthcare). We have previously validated this technique against cardiac output as a measure of circulation time in patients with sleep apnea, with and without HF. The changes in Sao2 from both the peak Sao2 and the Sao2 at the end of the apnea to the nadir in Sao2 following apnea termination for each apnea-hyperpnea cycle were calculated. The desaturation time, the rate of change in Sao2 per second from the end of the apnea to the nadir was calculated. Ten consecutive apnea-hyperpnea cycles during the first and last episode of stage 2 sleep were analyzed in each subject.
Timing of VPBs
The ECG was sampled at a frequency of 1000 Hz. The ECG tracing during all stages of sleep was inspected for the presence of VPBs. The QRS complexes were scored as VPBs if they were (1) premature, (2) not preceded by a premature P wave, (3) > 0.12 s in duration, and (4) of different morphology from those arising from sinus beats. VPBs were identified as occurring during the apneic or hyperpneic phase during episodes of recurrent central or obstructive apneas for total sleep time and for stage 2 sleep. The frequency of VPBs during apneas and hypopneas was compared with that during hyperpneas for patients with OSA and CSA.
Data were expressed as the mean ± SEM. Statistical analysis was performed using a statistical software package (SPSS, version 13.0; SPSS Inc; Chicago, IL). Continuous variables for the patients with OSA or CSA were compared using two-tailed unpaired t tests for variables with normally distributed data, the Mann-Whitney rank sum test for variables with nonnormally distributed data, and the Fisher exact test for nominal variables. VPB frequency and timing were assessed for within-group differences using paired t tests. Comparisons between the OSA and CSA groups were performed using the analysis of covariance to adjust for baseline differences in VPB frequency. A p value of < 0.05 was considered to be statistically significant.Tags: congestive heart failure, sleep-disordered breathing, Ventricular Arrhythmias