(12-25-2014, 03:50 PM)Kadenz Wrote: Is it better (in some sense & adjusting for size & weight) to breathe quickly or slowly; and deeply or shallowly?
(12-25-2014, 05:46 PM)PaytonA Wrote: My opinion is that it does not really matter as long as you are getting sufficient oxygen to your lungs. It would seem to me like the minute ventilation (the volume of air that gets to your lungs each minute) is the important thing.
(12-25-2014, 11:38 PM)PaytonA Wrote: The dependence of the correct tidal volume on height and correct weight does not make much sense to me. I would think that the heavier one is the more air is needed to oxygenate all of the tissues and that also takes me back to thinking that minute ventilation is probably more important.
Only a percentage of the air in each breath (in each Tidal Volume) reaches our alveoli and participtes in getting oxygen into our blood.
The percentage of air which does not reach the alveoli is the percentage of air which reaches only the nasal cavity and throat and bronchial tubes, which represent "dead space" as far as breathing is concerned.
A few comments:
1. The more shallowly we breathe, the larger is the proportion of air which stays in the dead space. For example, if we purposely breathe very shallowly, so that the Tidal Volume is smaller than the dead space in our airway, we would feel smothered and would be getting too little oxygen no matter how quickly we breathe these too-shallow breaths, because we would be rebreathing the air in our airway rather than breathing deeply enough to bring fresh air into our alveoli. So, in view of this, it can be said that it would be better to breathe deeper breaths more slowly instead of shallower breaths more quickly, even if the Minute Ventilation were to be the same.
2. In the formula given earlier, the expected Tidal Volume is calculated using a person's "ideal weight" which is based only on a person's height. So, essentially, this means the formula uses only our height or skeletal structure, which apparently is a better predictor of airway and lung volumes than weight. When people become overweight, their airway and lung size tend to stay unchanged. Also, I think fat cells do not need ventilation, or not as much as muscles and organs do.
Some types of ventilators target a certain amount of Tidal Volume. In an earlier post I linked to a thread which mentioned that sometimes overweight patients have been severely harmed when hospital staff have set up hospital ventilators to force too large of a Tidal Volume, because mis-trained hospital staff used the patient's actual weight instead of ideal weight when calculating the target Tidal Volume.
3. The ResMed ASV machines use Minute Volume to keep track of how much ventilation the patient needs, and when a patient fails to breathe the machine targets (tries to maintain) 90% of the patient's recent Minute Ventilation. So, clearly, ResMed medical staff agree with PaytonA that Minute Vent is more important than Tidal Volume alone.