Investigation Of End-tidal Carbon Dioxide (ETCO₂) And Heart Rate Variations During Sleep Apnea
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Sleep Apnea is a sleep disorder where limitation or cessation of breathing occurs. It is characterized by abnormalities in the respiratory pattern and quantity of ventilation during sleep. According to a study 4% of men and 2% of women have sleep apnea, which is a sizable sector of the adult population. To analyze end-tidal CO₂ and heart hate variations due to apnea, 8 hr polysomnography (Sleep Consultant. Inc, Fort Worth, Texas) was performed on limited sleep apnea subjects and breath hold maneuvers were performed in awake subjects. In the simulated apnea study, 16 volunteer subjects (age: 29 ± 5 yrs, BMI: 24 ± 5 kg/m2, 9 Male and 7 Female) were recruited to participate in two experimental protocols, referred to as A and B. Both A and B protocols involved breath hold maneuvers in sitting as well as supine positions. The order of protocols and the positions within the protocols were randomized. Each protocol started with normal breathing and stable blood pressure for 60s, followed by voluntary breath hold that lasted as long as the subject could tolerate. In A, each breath hold was followed by 90s of recovery; in B this period was 30s. The cycle was repeated five times in both protocols. The features extracted from the wave forms are End-Tidal CO₂, Exhaled Carbon dioxide concentration sum (ECCS), Inspiration Time/ Expiration Time Ratio, Peak-Peak Interval, and Heart Rate (ECG). The Mixed Linear Model and the Tukey Kramer analysis show that etco2, IE ratio from CO₂ and heart rate from ECG respectively are significant parameters (P < 0.05) to distinguish apneic events both in simulated and sleep study. ETCO₂ changes from baseline (40.80 ± 2.4) mmHg to normal breathings (38.56 ± 3.2) mmHg for sitting A which follows the same for other protocols. IE ratio changes from baseline (0.85 ± 0.05) to normal breathings (0.80 ± 0.06) for sitting A which follows the same for other protocols. Heart Rate changes from baseline (1.32 ± 0.02) *60 b.p.m to breath holds (1.26 ± 0.02) *60 b.p.m for sitting A which follows the same for other protocols. During sleep study there is a significant change in ETCO₂ from normal breathings (40.85 ± 3.9) mmHg to apnea (43.57 ± 3.4) mmHg and hypopnea (39 ± 6.4) mmHg. There is a significant change in IE ratio from normal breathings (1.58 ± 1.58) to apnea (1.02 ± 0.66) and hypopnea (1.21 ± 0.62). Heart Rate is also significantly different from normal breathings (1.05 ± 0.28) *60 b.p.m to apnea (1.19 ± 0.5) *60 b.p.m and hypopnea (1.06 ± 0.31) *60 b.p.m. It implies that during the apneic events the accumulation of CO₂, change in breathing patterns (IE ratio) and change in heart rate are significantly different. The posture (effect of gravity), frequency of apnea (protocols), duration of the breath hold did not have any effect on these features. Gender had an effect on the ETCO₂. These significant features can be used to check the efficacy of apnea treatment.