The questions raised here prompted me to do a little research. This information is abstracted from several Wikipedia articles and other technical articles found using Google.
Minvent (minute ventalation) is the total amount of air exchanged by the lungs during a one minute period. The tidal air volume is the amount of air exchanged by the lungs in a normal breath. I suspect the minvent value is calculated by sv machines which track the number of breaths per minute and the tidal air volume.
i.e. Minvent = breaths per minute X tidal air volume
Tidal air is a function of chest dimentions. Men, being generally physically bigger than women, have larger tidal volumes. Breaths per minute vary, going up with excercise and excitement and down with rest and relaxation.
Some of the "normal" ranges for these measurements reported in the articles are:
resting breaths per min = 12 to 20
resting minvent = 5 to 10 liters per minute
tidal air (for men) = approx 500 ml per minute = 0.5 liters per minute
tidal air (for womwn) = approx 350 mi per minute = 0.35 liters per minute.
So if alarms are going off there are several posibilities. 1) low or zero breaths per minute; 2) very shallow breathing; 3) machine malfunctions. Also, the point at which the alarm should trigger suggested by these reports is probably just below 5 liters per minute. Here I make my disclaimer that I am not a doctor or a technician so please DO NOT rely upon my analysis to alter your machine settings.
I use a Respironics bipap autoSV advanced with the Encore Pro Smart Card. I also have the Encore Pro 2.2 software to read the smart card. My machine reports my average breaths per minute for the past week = 17.1 and the average minvent = 8.9 liters per minute. Working backwards, my calculated tidal air volume is appro. 520 ml.
i.e. 520ml = 8900ml divided by 17.1 breaths per minute
I hope this analysis helps.
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