Pulmonary Function Tests: Spirometry and Alveolar Ventilation (Nursing)

00:02 So how do we actually test pulmonary function? We are able to test our pulmonary function using spirometry.

00:11 And usually this is able to distinguish between obstructive pulmonary diseases and restrictive diseases.

00:18 And an obstructive pulmonary disease, you're going to have an increased airway resistance because of some type of obstruction such as with bronchitis.

00:29 In these diseases are total lung capacity our functional residual capacity and our residual volume may all increase because of hyperinflation of the lungs.

00:44 In restricted diseases, we're actually going to have a reduced total lung capacity due to some type of disease or exposure to an environmental agent.

00:56 And this are vital capacity our total lung capacity are functional residual capacity and our residual volume are all going to decline because long expansion is compromised.

01:11 Usually in restricted diseases we have a restriction or a reduction in our lung compliance.

01:20 So our pulmonary function tests can measure the rate of gas movement in our lungs.

01:27 First, we have our forced vital capacity or FVC.

01:32 And this is the amount of gas that is forcibly expelled after taking a deep breath.

01:41 We measure this using the forced expiratory volume, which is the amount of gas expelled during a specific time interval of the forced vital capacity.

01:52 So for example, an FEV1 is the amount of air expelled in the first second of a forced exhalation.

02:02 And a healthy individual you're usually able to expel about 80% of your forced vital capacity in the first second.

02:12 But when you have an obstructive disease you exhale less than the 80% because there's some type of blockage and in a restrictive disease you usually are going to actually exhale more even when you have a reduced forced vital capacity.

02:30 And the why it's more is because the overall lung compliance is now low so that forced vital capacity or the denominator and our percentage is decreased while the force expiratory volume in that first second remains the same.

02:48 So therefore it will still be a higher percentage.

02:52 So we can also look at alveolar ventilation by looking at our minute ventilation or the total amount of gas that flows into or out of the respiratory tract in one minute.

03:04 Normally at rest.

03:06 This is going to be about 6 liters per minute when we're exercising, however, this can go up to as much as 200 liters per minute.

03:18 But this is only really a rough estimate of our respiratory efficiency and a better indicator is our alveolar ventilation rate our AVR and which case we're looking at the flow of gases into and out of the alveoli during a particular time.

03:36 So our alveolar ventilation rate takes into account the amount of dead space as well as the title volume and the rate of breathing and it can be calculated.

03:47 By looking at AVR equals the frequency of our breaths our respiration rate and our tidal volume.

03:56 Because the dead space in an individual is normally constant the only two things we really look at are the tidal volume and the frequency or the respiration rate.

04:07 Significant increases and our AVR can be brought about by increasing the title volume more so than increasing the frequency.

04:18 So for example, rapid shallow breathing can actually cause a decrease not an increase in alveolar ventilation rate.

04:28 So let's take a closer. Look at that.

04:31 So let's say at a normal rate and depth you have a title volume of about 500 milliliters and a respiratory rate of about 20 breaths per minute.

04:44 This would give you a minute ventilation or MVR of about ten thousand milliliters per minute.

04:51 And then, if we take all of these and put them together with an alveolar ventilation rate of 7,000 you would have an effective ventilation of out 70%.

05:05 If I change in all of a sudden started do doing slow and deep breathing where I'm going to decrease my respiratory rate, but I'm going to increase my title volume I'm actually going to end up with an effective ventilation that is higher than at the normal rate.

05:26 Conversely, if I look at my rapid shallow breathing where instead my tidal volume is really small and my respiratory rate is really fast.

05:37 I actually have a decrease in my effective ventilation to 40% compared to the normal rate.