Journal of applied physiology
-
To estimate the contributions of the heterogeneity in regional perfusion (Q) and alveolar ventilation (V A) to that of ventilation-perfusion ratio (V A/Q), we have refined positron emission tomography (PET) techniques to image local distributions of Q and V A per unit of gas volume content (sQ and sV A, respectively) and V A/Q in dogs. sV A was assessed in two ways: 1) the washout of 13NN tracer after equilibration by rebreathing (sV A(i)), and 2) the ratio of an apneic image after a bolus intravenous infusion of 13NN-saline solution to an image collected during a steady-state intravenous infusion of the same solution (sV A(p)). SV A(p) was systematically higher than sV A(i) in all animals, and there was a high spatial correlation between sQ and sV A(p) in both body positions (mean correlation was 0.69 prone and 0.81 supine) suggesting that ventilation to well-perfused units was higher than to those poorly perfused. ⋯ We conclude that, in the prone position, gravitational forces in blood and lung tissues are largely balanced out by dorsoventral differences in lung structure. In the supine position, effects of gravity and structure become additive, resulting in substantial gravitational gradients in sQ and sV A(p), with the higher heterogeneity in V A/Q caused by a gravitational gradient in sQ, only partially compensated by that in sV A.
-
Respiratory input impedance (Zin) over a wide range of frequencies (f) has been shown to be useful in determining airway resistance (Raw) and tissue resistance in dogs or airway wall properties in human adults. Zin measurements are noninvasive and, therefore, potentially useful in investigation of airway mechanics in infants. However, accurate measurements of Zin at these f values with the use of forced oscillatory techniques (FOT) in infants are difficult because of their relatively high Raw and large compliance of the face mask. ⋯ The power spectrum of oscillatory flow when the HIT was used showed amplitudes that were at least 100 times greater than those when FOT was used, increasing at f > 400 Hz. In conclusion, the HIT enables the measurement of high-frequency Zin data ranging from 32 to 800 Hz with particularly high flow amplitudes and, therefore, possibly better signal-to-noise ratio. This is particularly important in systems with high Raw, e.g., in infants, when measurements have to be performed through a face mask.
-
The AM-5600 is a new device that simultaneously monitors electrocardiogram (ECG) and noninvasive blood pressure (BP) over a 24-h period. BP readings (Korotkoff sounds and cuff air pressure) are stored into the recorder, allowing the removal of BP artifacts after a visual check. In 12 subjects with essential hypertension, we compared BP values simultaneously provided by the AM-5600 and intra-arterial recordings. ⋯ Editing removed 22.1% of total readings, slightly reducing between-method discrepancies. Thus the AM-5600 provides an accurate average estimate of resting and ambulatory SBP and, for DBP, a less accurate estimate that is slightly improved by editing. The AM-5600 allows accurate description of SBP and DBP profiles and thus may be suitable to describe the abrupt BP changes accompanying a number of clinical events.
-
Randomized Controlled Trial Comparative Study Clinical Trial
Acute mountain sickness: increased severity during simulated altitude compared with normobaric hypoxia.
Acute mountain sickness (AMS) strikes those in the mountains who go too high too fast. Although AMS has been long assumed to be due solely to the hypoxia of high altitude, recent evidence suggests that hypobaria may also make a significant contribution to the pathophysiology of AMS. We studied nine healthy men exposed to simulated altitude, normobaric hypoxia, and normoxic hypobaria in an environmental chamber for 9 h on separate occasions. ⋯ By lowering the barometric pressure and adding oxygen, we achieved normoxic hypobaria with the same inspired PO2 as in our laboratory at normal pressure. AMS symptom scores (average scores from 6 and 9 h of exposure) were higher during simulated altitude (3.7 +/- 0.8) compared with either normobaric hypoxia (2.0 +/- 0.8; P < 0.01) or normoxic hypobaria (0.4 +/- 0.2; P < 0.01). In conclusion, simulated altitude induces AMS to a greater extent than does either normobaric hypoxia or normoxic hypobaria, although normobaric hypoxia induced some AMS.
-
Regional ventilation and perfusion were studied in 10 anesthetized paralyzed supine patients by single-photon emission computerized tomography. Atelectasis was estimated from two transaxial computerized tomography scans. The ventilation-perfusion (V/Q) distribution was also evaluated by multiple inert gas elimination. ⋯ Little perfusion was seen in the most ventral parts (zone 1) of caudal (diaphragmatic) lung regions. In summary, shunt during anesthesia is due to atelectasis in dependent lung regions. The V/Q distributions differ from those shown earlier in awake subjects.