Category Archives: Sleep Apnea

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (17)

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (17)With the usage of nasal CPAP, an effective treatment for OSAS, Pes nadir decreased significantly in our subjects. In OSAS patients, it also led to a disappearance of LSIVS and pulsus paradoxus and a significant increase in inspiratory LVIDd. As in acute asthmatic attacks, the appearance of pulsus paradoxus in OSAS patients can serve as a valuable index. Its appearance indicates a marked increase in Pes nadir, and its disappearance with nasal CPAP may be one of the signs of effective treatment of obstructive sleep apnea.

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (16)

2.    There is an increased filling of the right ventricle during the inspiratory effort against a closed upper airway, with displacement of the interventricular septum. As shown in our study, this will limit the filling of the left ventricle by reducing its compliance, thus lowering left ventricular stroke volume and decreasing the arterial blood pressure during inspiration. It is also possible that the abnormal systolic motion of the interventricular septum during inspiration may have the same action without compliance changes.

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (15)

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (15)They may also be related to the data obtained from animals and humans which show that, during the Muller maneuver, hemodynamic alterations are induced by markedly rifegative pleural pressure.
Our investigation is the first clear demonstration that pulsus paradoxus, ie, a fall in systolic pressure of more than 10 mm Hg during inspiration, can be present during obstructive sleep apnea, in association with significant end-diastolic negative Pes. Pulsus paradoxus can be noted in breathing disorders during wakefulness, such as severe asthma and chronic airway disease. Settle et al observed in COPD patients that the inspiratory effort apparently causes overdistension of the right ventricle, which in turn displaces the interventricular septum posteriorly into the left ventricle, possibly impairing the filling of the left ventricle.

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (14)

Almost all the abnormal septal motions detected during our study were type B rather than type A, and the greatest abnormal septal motion was seen when the most negative Pes nadir coincided with end-diastole. In half of our population, the septal motion, when analyzed qualitatively, was clearly paradoxic, (LSIVS). The LSIVS -I- patients were significantly younger and also had more negative Pes nadirs than the other subjects. During NREM sleep, contraction of diaphragmatic and intercostal muscles increased during inspiratory effort, and this increase was responsible for the increase in Pes nadir. We hypothesize that younger individuals may have greater muscle strength and may be able to induce more inspiratory effort against a closed glottis than older individuals, such as those in the LSIVS — group. Right ventricular volume has been shown to increase during obstructed inspiration and a significant increase in Pes nadir. The LSFVS may thus result from a transient right ventricular volume overload temporally related to the strong inspiratory effort performed with a partially or completely obstructed airway.

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (13)

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (13)Discussion
Understanding the hemodynamic abnormalities associated with obstructive sleep apnea are of importance, considering the cardiovascular morbidity and mortality associated with OSAS which already has been reported. As reported before and as seen here, some OSAS patients can develop very negative Pes values during Muller maneuvers (as low as —80 cm H20 in our study, for example). Left ventricular end-diastolic volume, or preload, is thought to be reduced through ventricular interdependence mechanisms.

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (12)

Limitations of the Investigation
Undoubtedly, the more equipment fitted to a subject, the more disturbed his or her sleep may be, and certain sleep states may not occur. In five patients, we were unable to obtain an REM sleep period sufficiently long for echocardiographic study, and the sleep disturbance led two subjects to request discontinuation of the arterial blood pressure line. We did obtain good measurements in all individuals during NREM sleep. Echocardiographic signals were obtained during apneic events, even in cases of significant obesity, since subjects had very low lung volumes and very limited movement. This absence of air exchange allowed great reduction in artefacts related to cardiac movements. However, signal distortions existed during the post-apneic hyperventilation period, due to hyperventilation and movements. It also must be noted that recent transesophageal echo-Doppler investigation of 36 non-apneic patients treated with PEEP of 20 cm H20 demonstrated absence of abnormal interventricular septum motion (Popp, personal communication).

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (11)

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (11)There was no significant difference in Pes nadir between breathing while awake and supine and unobstructed breathing during sleep with nasal CPAP Similarly, no significant difference was seen when LVIDd, LVIDs and RVIDd were measured during wakeful supine breathing, NREM sleep breathing with nasal CPAP and REM sleep breathing with nasal CPAP Nasal CPAP led to normal, unobstructed breathing, a significant decrease in Pes nadir and an improvement of lowest SaO£ in all subjects. As can be seen in Table 2, when baseline and nasal CPAP echocardiographic measurements were compared for the entire group, the results were nonsignificant, despite the trend. But when LSIVS + patients were investigated separately, there was a disappearance of LSIVS and pulsus paradoxus with nasal CPAP.

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (10)

Pulsus paradoxus was defined as an inspiratory (or inspiratory effort against a closed upper airway) decrease in systolic blood pressure of 10 mm Hg or more. Pulsus paradoxus was noted with simultaneous significantly negative Pes nadir and associated LSIVS during obstructed breathing (Figs 3 and 4). The most important falls in systolic blood pressure during obstructed breathing were in subjects 1 to 3; their values were 28, 25 and 30 mm Hg, respectively. None of the patients had clinical evidence suggesting pericardial restriction or echocardiographic evidence of pericardial effusion.

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (9)

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (9)Figure 1 shows an M-mode echocardiographic recording made during an obstructive sleep apnea in stage 2 NREM sleep. Figures 2 to 4 show the simultaneous evolution of Pes, radial arterial blood pressure and Sa02 during baseline obstructive sleep apnea and in the same subject during unobstructed breathing with nasal CPAP. As can be seen, LVIDd and LVIDs decreased gradually with increasingly negative Pes nadir. We looked at the Pes values corresponding to points of end-diastole, since end-diastole is the point at which a collapse due to LSIVS is likely to occur.

Leftward Shift of the Interventricular Septum and Pulsus Paradoxus in Obstructive Sleep Apnea Syndrome (8)

Results
All patients presented with symptoms of obstructive sleep apnea, but RDI and lowest Sa02 values during sleep varied, as indicated in Table 1. The greatest difference was in maximum Pes nadir during sleep, which oscillated between — 4 and —80 cm H20. The mean values of the different measurements taken with and without nasal CPAP are presented in Table 2.

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