This invention relates to a method of evaluating data pertaining to respiration and heart beat and an apparatus for evaluating them, especially for forecasting sudden infant death syndrome (SIDS) by investigating the correlation between respiration and heart beat in a normal state and respiratory standstill in sleep.
Generally, the data from organisms includes EEG, cardiac electricity, respiration, ocular movement, and EMG. Signal forms of this data are relatively more useful than from EEG etc. It is therefore easier to analyze an R--R interval as a change of peak interval of an ECG wave, chronologically.
Considering that respiratory arrhythmia depends upon an efferent impulse from an extension receptor, standstill of the efferent impulse from an extension receptor in respiratory arrest in sleep will have an effect on heart beat. It has been already reported that in Cheyne Stokes respiration during hyperrespiration the increase of heart beat and decrease of blood pressure are observed; during its apnea the decrease of heart beat and increase of blood pressure occur.
Here, sleep-apnea syndrome is defined as three following cases:
(1) At least 30 episodes of apnea appear in the night sleep of 7 hours.
(2) An apnea episode appears in REM-sleep as well as in non-REM-sleep.
(3) An episode of apnea has a tendency to appear continuously.
The classification of sleep apnea syndrome according to Gastant is divided into the three following types
(1) Central type: A respiratory standstill at the nostrils and mouth appears along with the disappearance of thoracid and abdominal movements. This indicates the stoppage of activity of the respiratory center.
(2) Obstructive or upper tracheal type: In spite of respiratory efforts by thracic and abdominal movements, respiration stops, suggesting an obstruction in the upper tracheal tract.
(3) Mixed type: An intermediate type between central and obstructive ones. Although at the first phase of apnea the thracic and abdominal movements cease, its symptom becomes more severe gradually.
In the central type, the apnea episode often appears repeatedly in an almost constant period, frequently observed in non-REM-sleep, but in the obstructive type an apnea episode appears at various intervals and its duration is also not constant. Also, in the central type, during hyperventilation in Cheyne Stokes respiration an increase of heart beat is observed. During the apnea phase its decrease and a periodical change are noticed.
The mechanism of the central type of sleep-apnea can be explained by neurogenous or respiratory disturbance theory. The neurogeneous theory is based on the assumption that there is an oscillation center in the brainstem, and an inhibitory mechanism for controlling oscillation in the forebrain. The respiratory disturbance theory rests on the basis that a respiratory disturbance delays a feed-back loop between the respiratory center and chemical receptor, and an oscillation phenomenon appears.
It has not been determined which effect really works, or whether both effects work simultaneously.