Search PubMed⌕ Search

Biomedical subjects

J W Watson

Publications and source records attributed to J W Watson.

At least 55 records · Page 3Linked to original sources
PubMed1985

Coronary artery atherosclerosis observed in men over 14 consecutive years.

The incidence of cardiovascular death and myocardial infarction associated with ischemic heart disease has declined over the past 15 years. Whether this is associated with a decrease in the severity of coronary atherosclerosis is unknown. The extent of coronary atherosclerosis in men was determined by postmortem coronary angiography in 505 patients over an observation period of 14 years. Patients were divided into those with ischemic heart disease (42%) and those without (58%). Mean coronary scores showed no significant trends over the 14-year period in those without ischemic heart disease and for the last 10 years in those with ischemic heart disease. In those few patients evaluated early in the study with ischemic heart disease, a significantly lower coronary score was found compared to subsequent years. This study was performed during an era of declining cardiovascular death rates and a declining incidence of myocardial infarction, and suggests that this decline may relate to favorable changes in pathogenesis rather than to a decrease in extent of coronary atherosclerosis.

Adult↗
PubMed1985

CO2 elimination as predicted by augmented dispersion and convection in an asymmetrical dog airway model.

We have developed a computer model of the dog lung based upon an asymmetrically branching network of tubes to describe gas exchange during high-frequency oscillations. Impedances to oscillatory flows were calculated for each airway segment and used to determine flow distributions in all airway generations. Gas exchange was assumed to occur by convective and augmented dispersive mechanisms. Also included in the model were features commonly found in animal studies including the effects of bias flow of fresh gas at the airway opening and equipment dead-space volume. The magnitude of CO2 elimination predicted by the model closely resembled actual experimental data. Specifically, it predicted that CO2 elimination is proportional to frequency to the 0.82 power and tidal volume to the 1.25 power. It also indicated that the bias flow rate and equipment dead-space volume influence gas exchange characteristics and thus these variables should be considered when comparing data from different studies.

Airway Resistance↗
PubMed1985

Frequency dependence of CO2 elimination and respiratory resistance in monkeys.

In dogs, respiratory system resistance (Rrs) is frequency independent, and during high-frequency oscillatory ventilation (HFO) the relationship between CO2 elimination (VCO2) and frequency is linear. In contrast, we found in rabbits a large frequency-dependent decrease in Rrs with increasing frequency along with a nonlinear relationship between frequency and VCO2 (J. Appl. Physiol. 57: 354-359, 1984). We proposed that frequency dependent mechanical properties of the lung account for inter-species differences in the frequency dependence of gas exchange during HFO. In the current study we tested this hypothesis further by measuring VCO2 and Rrs as a function of frequency in a species of monkey (Macaca radiata). In these monkeys, Rrs decreased minimally between 4 and 8 Hz and in general increased at higher frequencies, whereas VCO2 was linearly related to frequency. This is further evidence supporting the hypothesis that nonlinear frequency-VCO2 behavior during HFO is related to frequency-dependent behavior in Rrs.

Airway Resistance↗
PubMed1984

CO2 elimination and airway opening pressure during high frequency oscillation in dogs.

CO2 elimination (VCO2) and pressure at the airway opening (Pao) were measured over a wide range of frequencies (f) (5-40 Hz) and tidal volumes (VT) (1-45 ml) during high frequency oscillatory ventilation (HFO) in 11 anesthetized, paralyzed dogs. CO2 elimination was found to depend primarily on the product off and VT which is consistent with theoretical predictions of gas exchange by augmented dispersion. Airway opening pressures during HFO were frequency dependent. At frequencies near 5 Hz Pao was lower, while at frequencies above 5 Hz Pao was higher than Pao during conventional mechanical ventilation (12 cm H2O). The minimum Pao (5 cm H2O) achieved while maintaining VCO2 equivalent to normal metabolic CO2 production occurred when VT was near that of the dead space volume and frequency was near 5 Hz. At lower VT, higher frequencies were required to maintain VCO2 and this increased frequency resulted in an increase in Pao amplitude (10-15 cm H2O).

Animals↗
PubMed1984

Oscillatory mechanics of the respiratory system in ozone-exposed rats.

The respiratory system impedance of tracheostomized cardiorespiratory disease-free Sprague-Dawley rats was measured from 20 to 90 Hz at constant flow amplitudes in 10 rats exposed to 0.64 ppm (UV) ozone for 7 days, and eight rats exposed to the same level of ozone for 20 days. This data was compared with respiratory system impedence spectra of 24 normal rats obtained in the same manner. When compared with control, the real part (effective resistance) was significantly different at several frequencies in the 7-day group (P less than 0.05), and group means were higher at all frequencies. The 20-day group showed no significant differences in effective resistance. The imaginary part (effective reactance) was significantly lower at higher frequencies (f greater than 36) in both exposure groups (P less than 0.05). When the impedance curves for each individual were fit to a lumped six-parameter model, and the parameters were compared, only the peripheral resistance parameter of the 7-day group was significantly different from control (P less than 0.05). We conclude that ozone exposure at this level causes changes in respiratory system impedance, that these changes consist primarily of decreased reactances at higher frequencies, and that at 7 days these changes can be modeled by an increase in peripheral resistance.

Airway Resistance↗
PubMed1984

Respiratory system, lung, and chest wall impedances in anesthetized dogs.

We measured impedances of the respiratory system (Zrs) and lung (ZL) in anesthetized and paralyzed dogs at frequencies between 4 and 64 Hz. Zrs was measured at functional residual capacity (FRC) and with mean transpulmonary pressures (Ptp) of 12 and 30 cmH2O; ZL was measured with the chest wall open at FRC and Ptp = 12 cmH2O. From these data we derived chest wall impedances at FRC and 12 cmH2O. Effective resistances of the respiratory system, lung, and chest wall were all frequency dependent. At frequencies below 22 Hz frequency dependence of respiratory system resistance was due to the frequency dependence of the chest wall, whereas at higher frequencies it was due to frequency dependence of the lung. Analysis of the impedance data between 4 and 32 Hz provided estimates of resistance, inertance, and compliance of the lung, chest wall, and respiratory system. At FRC, 41% of the respiratory system resistance was due to the lung and 59% was associated with the chest wall. Nearly all of the respiratory inertance (98%) was due to the lung. Lung compliance was approximately twice that of the chest wall, the former accounting for approximately one-third of respiratory elasticity. As lung volume was increased, respiratory resistance and compliance decreased; inertance also decreased, although this change was not significant.

Airway Resistance↗
PubMed1984

CO2 elimination as a function of frequency and tidal volume in rabbits during HFO.

CO2 elimination (VCO2) was monitored during high-frequency oscillation (HFO) over a frequency (f) range of 2-30 Hz in anesthetized and paralyzed rabbits to determine whether effective gas exchange could be achieved in this species, to determine the f and tidal volume (VT) dependence of gas exchange in this species, and to compare these results with those from dog and human studies. We were able to produce VCO2 levels during HFO that exceeded normal steady-state levels of CO2 production with VT's less than the total dead space volume. VCO2 was related to f in a curvilinear fashion, whereas in some rabbits VCO2 became independent of f at higher frequencies. This curvilinear relationship between f and VCO2 is similar to data from humans but contrasts with the linear relationship found in dogs. Evidence is presented indicating frequency-dependent behavior of gas exchange is correlated with a frequency-dependent decrease in respiratory system resistance. We propose that the frequency-dependent mechanical properties of the rabbit lung may also account for the species differences in HFO gas exchange.

Animals↗
PubMed1983

Technique for making hollow central airway casts.

We have developed a method for producing rigid hollow casts of the central airways. Woods metal (melting point 70 degrees C) was poured into the airways at the trachea of an excised canine lung air-dried at a transpulmonary pressure of 30 cmH2O. The tissue was dissolved and removed, and the resulting negative cast was carefully trimmed leaving only airways with a diameter of 2 mm or greater. The cast was then electroplated with copper that provided a rigid jacket encasing the Woods metal. Heating this structure to 100 degrees C liquefied the Woods metal allowing the majority of it to flow out. Residual amounts were readily removed by a high-pressure steam hose attached to the trachea. Comparisons were made between airway diameters from in vivo radiographic bronchograms (DB) and direct measurements of the resulting trimmed Woods metal cast (DC). Linear regression analysis of these data indicated a high degree of correlation (DC = 0.98 DB + 0.03, r = 0.99). We concluded that this technique produces positive casts which provide a good representative model of the central airways.

Animals↗
PubMed1982

Oscillatory mechanics of the respiratory system in normal rats.

Respiratory system impedances were measured by a modified forced oscillatory technique in 30 normal male CRD-free Sprague-Dawley rats at frequencies between 20 and 90 Hz. A resonance frequency was found (mean = 39 Hz) below which reactances were negative and above which reactances were positive. Resistances were generally found to be frequency dependent, increasing with increasing frequencies. Frequency dependent behavior in resistance has been ascribed to inhomogeneities in parallel airway pathways and to the effects of airway wall compliance. optimization techniques were used to estimate the values of parameters in a variety of lumped-parameter mechanical networks incorporating parallel pathways and/or airway wall compliance. The model whose response compared the best with the data and that resulted in the most consistent parameter values was found to be one where the airways are separated into central and peripheral components by a shunt pathway containing an airway wall compliance. The mean values for each of the parameters within the model were central airway resistance (54 cm H2O/L/sec), peripheral airway resistance (53 cm H2O/L/sec), central airway inertance (0.058 cm H2O/L/sec2), peripheral airway inertance (0.116 cm H2O/L/sec2)(, airway wall compliance (0.182 X 10(-4) L/cm H2O), and respiratory system compliance (1.267 X 10(-4) L/cm H2O).

Airway Resistance↗
PubMed1982

Rate dependent variation in concealed bigeminy.

A 63 year old man with angina pectoris was found to have frequent extrasystoles separated by odd as well as even numbers of conducted sinus beats. Analysis of 935 conducted sinus beats showed that premature ventricular beats without interpolation were separated by odd numbers of conducted sinus beats in 117 sequences and even numbers (exceptions) in 48 sequences (p less than 2 X 10(-4)). Tabulation of cycle lengths revealed that cycles with even numbers of conducted sinus beats were characterized by a significant reduction in the preceding postextrasystolic pause (1441+/-76 msec vs. 1487 +/-59 msec; p less than .001) and second sinus cycle (720 +/- 44 msec vs. 750 +/- 38 msec; p less than .001). Premature ventricular beats were interpolated in 41 additional sequences. Interpolated extrasystoles were separated by the expected even numbers of conducted sinus beats in 39 cases and odd numbers (exceptions) in only two cases. The frequency of exceptions to the usual rules for concealed bigeminy was therefore 2/39 during interpolation and 48/117 without interpolation (p less than .01). This case demonstrates that: 1) a reduction in cycle length may be associated with exceptions to the usual rules for concealed bigeminy, and 2) the frequency of exceptions to concealed bigeminy may be altered by the presence of interpolation. Only one previous case has contained statistical documentation of these circumstances. The diagnosis of a concealed ventricular rhythm may be facilitated by careful analysis at multiple cycle lengths.

Angina Pectoris↗
PubMed1980

Sudden death in cardiomyopathy: role of bradycardia-dependent repolarization changes.

A 20-year-old man presented with cardiomegaly, frequent PVC's, and abdominal pain. On the nineteenth hospital day the patient developed ventricular fibrillation and died. Analysis of a Holter recording initiated 16 hours previously demonstrated an increase in the corrected QT interval (QTc) to 0.48 second and a prematurity index less than 1.0 only during the minute terminated by ventricular fibrillation. This report documents changes in sinus rate, coupling interval, QTc, and prematurity index for 16 hours preceding ventricular fibrillation in a patient with cardiomyopathy. The timing of the terminal arrhythmia coincided with significant changes in the QTc and prematurity index characterized by bradycardia-dependent QTc prolongation and a post-extrasystolic reduction in prematurity index.

Adult↗