Monitoring of asthma patients for bronchoconstriction has often relied on the use of pulmonary function tests such as the PEFR. Noninvasive attempts to measure respiratory obstruction have included the use of ear oximetry. Although oximetry is a useful method, it is insensitive except when severe abnormalities are present. It is therefore of limited value in moderate asthma. In the present study, no patient had significant desaturation while asleep.
Martin et al have documented the number of wheezing episodes, night and day, in hospitalized asthmatic patients. They found increased wheezing at night, using wheezing as a measure of airflow obstruction.
We have previously noted that wheeze duration (as a proportion of the respiratory cycle duration: Tw/Ttot) and frequency of the sound signal were associated with the degree of bronchospasm, but wheeze sound intensity was not. We have developed a computer algorithm to establish whether wheezes were or were not present during random samples of the breath cycle, and thus, to estimate the percentage of time in which wheezing occurs. This study demonstrates the correlation between this estimated Tw/Ttot and the level of airways obstruction observed.
Random segments of sound signal were studied to assure that there was no bias towards any portion of the respiratory cycle. A computer program was used to analyze each segment of the sound signal and determine whether a peak was present. However, analysis of sound signals must include other sounds recorded, such as those associated with body movement, speech, and external noises in the room. These noises could contain tones which could lead to mistaking a peak on sound signal analysis as a wheeze. Table 3 shows the results of varying the minimal peak associated with a wheeze. Using the most sensitive value may lead to noise being accepted as wheezing, and thus, an Est Tw/ Ttot which would be inappropriately high. The fact that a relationship is seen between the FEVi and the Est Tw/Ttot at the highest sensitivity is not surprising, since Forgacs et al have noted a correlation between noisy breathing heard at the mouth and obstructive airways disease. On the other hand, if we are too discriminating, we may reject peaks which do represent wheezes. This appears to occur when peaks are counted as wheezes only when nine or more times the baseline. Accepting as wheezes peaks which were three or more times baseline led to a good correlation with FEVX, as well as the one most sensitive to intersubject variation.
Wheezing depends on flow-rate and volume, and the five-minute sample contains breaths which vary in both of these respects. However, over a five-minute time period, this appears to even out. Different sets of 50 samples from a five-minute time period provide similar estimates of Tw/Ttot. Over 30 minutes, there was no significant change in the Est Tw/Ttot for different five-minute periods if the FE Vi remained the same. Do you need to substitute you previous ventolin inhaler? You may do it in one click with our web site – http://buy-asthma-inhalers-online.com/.
Asthma has been shown to follow a circadian pattern in some patients, with the worst obstruction occurring at around 4 am. Several possibilities have been suggested as a cause, including a rise in serum histamine levels with a fall in serum cortisol and epinephrine level.
Our studies are consistent and confirm the worsening of asthma at 4 am. This worsening of bronchospasm was demonstrated without awakening the patient, and therefore, could not be attributed to poor patient compliance in performing a test such as the PEFR.
In summary, we report a method of externally monitoring wheezes. Analysis of the lung sounds for the amount of wheezing in the breath cycle correlated with the FEVi. In the asthmatic patient, more wheezing was noted between 4:00 and 4:30 am than earlier in the evening.