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Biomedical subjects

M A Sackner

Publications and source records attributed to M A Sackner.

At least 37 records · Page 2Linked to original sources
PubMed1993

Tidal volume measurements in newborns using respiratory inductive plethysmography.

Respiratory inductive plethysmography (RIP) is a well-accepted noninvasive technology for monitoring breathing patterns in adults. Prior attempts to calibrate this device in babies have been fraught with technical difficulties, thereby limiting applications in this population. Recently, a new method, qualitative diagnostic calibration (QDC), has been shown to provide accurate calibration of tidal volume in adults. The QDC method is based upon principles of the isovolume maneuver and carried out during natural breathing without specialized respiratory maneuvers or postural changes. We calibrated RIP with QDC in the supine posture and compared tidal volume (VT) measured with RIP to VT by a face mask-pneumotachograph (PNT) in 21 healthy full-term newborns in supine and prone postures. Eleven of the babies were calibrated during active sleep and 10 in quiet sleep. The mean VT in the supine and prone postures were 19 and 25 ml, respectively. In the supine and prone postures, weighted mean difference between RIP (VT) and PNT (VT) and 95% confidence intervals were -0.05 ml (-0.27, 0.18) and -0.32 ml (-0.08, 0.55), respectively. There was no difference in the accuracy of RIP relative to PNT calibrated during active sleep when thoracoabdominal incoordination was present or quiet sleep when it was not in either the supine or the prone postures. Therefore, in full-term infants, RIP calibrated with QDC solely in the supine posture provides clinically acceptable measurements of VT in both supine and prone postures.

Analysis of Variance↗
PubMed1991

Noninvasive measurement of central venous pressure by neck inductive plethysmography.

Bedside estimation of the height at which the internal jugular veins collapse, referenced to a standard hemodynamic location, theoretically reflects central venous pressure. This method has never been demonstrated as accurate when compared to invasive CVP measurements because of the great clinical skills and time required to visually identify the internal jugular venous waveform. Since the principles of the bedside method are sound, we utilized them in conjunction with the neck inductive plethysmograph, a device which has the capability of recording internal jugular venous and carotid arterial waveforms. The respiratory distortion of these vascular waveforms was eliminated by employing a digital bandpass filter, making it easy to identify the venous and arterial waveforms on the videoscreen of a personal computer. The upper torso was positioned while observing the videoscreen until the vascular waveform was seen as a mixed arteriovenous waveform, signifying intermittent internal jugular venous collapse. The height of the internal jugular vein above the phlebostatic axis was obtained by external measurement and recorded as CVPni in cm H2O. In 43 patients, 86 percent of CVPni (NIP) values fell within 20 percent CVPi (invasive catheter measurements) over a range of CVP from 0 to 19 cm H2O. In an additional seven patients, CVPi was greater than the height that the upper torso could be elevated and an arterial waveform could not be obtained. Here, CVPni was recorded as the value at least exceeding the value measured. In two other patients, obstruction of an internal jugular vein gave spuriously low values of CVPni. Our study indicates that this new neck inductive plethysmographic method is accurate compared to invasive catheter measurements of CVP and should serve as a safe, noninvasive alternative in situations where such measurements are required.

Adult↗
PubMed1991

Thoracocardiography. Part 1: Noninvasive measurement of changes in stroke volume comparisons to thermodilution.

The thoracocardiograph (TCG) is a new noninvasive monitoring device that measures cardiac oscillations transmitted to the external surface of the thorax. It consists of 2.5 cm in height, elastic inductive plethysmographic transducers placed transversely in the proximity of the xiphoid process to provide changes in cross-sectional area on a transverse plane across the minor ventricular axis. Cardiac oscillations synchronous with each heart beat are extracted from the respiratory signal during breathing with an ensemble-averaging technique using the electrocardiograph as a trigger pulse. The average cardiac waveform at locations near the xiphoid process in normal humans has the appearance of a ventricular volume curve. The latter is also found in the majority of patients with heart disease although in some, outward (dyskinetic) rather than inward motion during systole occurs at one or more locations of the TCG transducers. As in echocardiography, such findings are consistent with ischemic or scarred myocardium invalidating computation of changes in stroke volume from such sites. In anesthetized dogs and critically ill patients with normal ventricular wall motion, changes in TCG derived ventricular volume waveform amplitudes agreed well with changes of thermodilution estimates of stroke volume during atrial pacing and fluid loading in the dogs on the one hand and with application of extrinsic positive end-expiratory pressure (PEEP) in patients on the other hand. Thoracocardiography has the potential for noninvasive, continuous monitoring of stroke volume and cardiac output as well as for detection of ischemic or scarred myocardium.

Aged↗
PubMed1991

Thoracocardiography. Part 2: Noninvasive measurement of changes in stroke volume; comparisons to impedance cardiograph.

The thoracocardiograph (TCG) displays cardiac oscillations transmitted to the external surface of the thorax through inductive plethysmographic transducers placed transversely around the thorax near or about the xiphoid process. Such signals, with the appearance of ventricular volume curves, were used to compute changes of stroke volume (SV) and cardiac output (CO) in normal subjects. Their values were compared with changes of SV and CO measured with the impedance cardiograph (IC). Increases of SV and CO were produced with subcutaneous terbutaline and there was excellent agreement between TCG and IC values, best from TCG transducers placed at the xiphoid process and 3 cm caudal to it, although TCG locations 6 cm caudad and 3 cm cephalad to the xiphoid were also satisfactory. Since the site 3 cm caudad to the xiphoid process is known to anatomically transect solely a segment of the left ventricle, it was designated the TCG-Reference location. Both TCG and IC derived SV were not altered during postural shifts about a horizontal axis. Neither TCG nor IC showed the expected large decreases of SV from supine posture to head-up tilt. With baseline TCG and IC measurements in 60 degrees head-up tilt. MAST suit application increased CO measured with TCG but not with IC. Neither TCG nor IC revealed alteration of CO with nasal CPAP up to 10 cm H2O despite a rise in functional residual capacity (FRC) level of 870 ml. This investigation indicates that TCG has promise as a near continuous, noninvasive monitor of SV and CO in normal subjects if postural axis is fixed and does not require highly trained personnel or labor-intensiveness for its operation.

Adult↗
PubMed1990

Pleural pressure changes in dogs measured from suprasternal fossa movements.

Movements of the suprasternal fossa during spontaneous breathing monitored with the surface inductive plethysmograph (SIP) have been shown to reflect changes of intrapleural pressure in conscious humans. Calibration of this device in anesthetized intubated dogs was accomplished by adjusting the electrical gain of its analog waveform to be equivalent to changes of airway pressure during inspiratory efforts against an occluded airway. This procedure, denoted the occlusion test, was also used to identify the site of esophageal balloon catheter placement for its recording of intrapleural pressure deflections. The validity of SIP-derived estimates of inspiratory and expiratory pulmonary resistances and lung compliance was established by finding close agreement with measurements obtained with intraesophageal pressure changes during 1) unimpeded spontaneous breathing, 2) inspiratory resistive loading, 3) bronchoprovocation with aerosolized carbachol, 4) mechanical ventilatory modalities, and 5) induced pulmonary edema. Therefore, movements of the suprasternal fossa with respiration can be reliably transformed into quantitative or semiquantitative changes of intrapleural pressure in anesthetized intubated dogs during major alterations of pulmonary mechanics.

Airway Resistance↗
PubMed1989

Calibration of respiratory inductive plethysmograph during natural breathing.

We describe a single-posture method for deriving the proportionality constant (K) between rib cage (RC) and abdominal (AB) amplifiers of the respiratory inductive plethysmograph (RIP). Qualitative diagnostic calibration (QDC) is based on equations of the isovolume maneuver calibration (ISOCAL) and is carried out during a 5-min period of natural breathing without using mouthpiece or mask. In this situation, K approximates the ratio of standard deviations (SD) of the uncalibrated changes of AB-to-RC volume deflections. Validity of calibration was evaluated by 1) analyzing RIP waveforms during an isovolume maneuver and 2) comparing changes of tidal volume (VT) amplitude and functional residual capacity (FRC) level measured by spirometry (SP) with RIP values. Comparisons of VT(RIP) to VT(SP) were also obtained in a variety of postures during natural (uninstructed) preferential RC and AB breathing and with voluntary changes of VT amplitude and FRC level. VT(RIP)-to-VT(SP) comparisons were equal to or closer than published reports for single posture, ISOCAL, multiple- and linear-regression procedures. QDC of RIP in supine posture with comparisons to SP in that posture and others showed better accuracy in horizontal than upright postures.

Calibration↗
PubMed1989

Enhanced aerosol deposition in the lung with mild airways obstruction.

We investigated the sensitivity of aerosol deposition to airways obstruction by measuring total deposition fraction of inert aerosol in normal conscious sheep (n = 6) after challenging cholinergic agent, pilocarpine (PL) (0.5 mg/kg intravenously) with and without a prior challenge of beta 2-adrenergic agonist, terbutaline sulfate (TS) (0.025 mg/kg subcutaneously). Aerosol deposition was measured by a light-scattering aerosol photometer in situ while sheep rebreathed 1.0-micron-diameter inert oil droplets from a 0.2-L collapsible bag at a rate of 30 breaths/min. Total accumulated deposition at the fifth breath (AD5) as a percentage of initial aerosol concentration was determined and compared with mean pulmonary airflow resistance (RL). After PL, both AD5 and RL increased significantly from baseline values by 51 +/- 9% and 597 +/- 118% (mean +/- SE), respectively, whereas AD5 and RL decreased significantly by 16 +/- 4% and 34 +/- 6%, respectively after TS (p less than 0.05). After PL subsequent to TS (TS-PL), AD5 increased in all six sheep by 33 +/- 7% from post-TS values (p less than 0.05). However, RL did not change from post-TS values. Greater changes in RL than in AD5 after PL (bronchoconstriction) or TS (bronchodilation) suggest a greater sensitivity of RL than AD5 to airway patency in the large airways. Lack of increase of RL after TS-PL indicates that bronchoconstrictive effect of PL was blocked by prior challenge with TS. Therefore, the increase in AD5 after TS-PL may be related to the peripheral airway obstructions which might have been caused by increased secretions induced by a potent secretagogue PL.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosols↗
PubMed1989

End-tidal carbon dioxide in critically ill patients during changes in mechanical ventilation.

Values of end-tidal CO2 (PETCO2) approximate PaCO2 in spontaneous breathing normal subjects and in stable patients receiving mechanical ventilatory support (MVS). Because marked inequality of ventilation/perfusion ratios in critically ill patients might affect this correlation, we assessed changes of PETCO2 in predicting changes in PaCO2 (delta PaCO2) and changes in minute ventilation (delta Ve) in this patient population. Twenty consecutive intubated patients 38 to 89 yr of age (mean, 70 yr) with respiratory failure while receiving MVS with indwelling arterial lines were studied. Settings on the mechanical ventilator were varied for frequency and tidal volume, and after a minimum of 5 to 10 min equilibration, PaCO2 and PETCO2 were measured. Vt and Ve were recorded from the digital indicator of the pneumotachygraph within the mechanical ventilator and corrected for compression volume in the respirator circuit. A total of 116 simultaneous measurements were performed. PETCO2 correlated well with PaCO2 (r = 0.78, p less than 0.001). The 95% confidence interval for the mean difference in PaCO2-PETCO2 was 4.0 +/- 0.97 mm Hg. However, delta PETCO2 (measured from baseline) did not correlate as well with delta PaCO2 (r = 0.58, p = less than 0.001). In four patients, the trend in their PETCO2 during changes in mechanical ventilation were in the opposite direction from the trend in their PaCO2. Thus, many critically ill patients, who cannto be preidentified, have an inconstant PaCO2-PETCO2 gradient with changes of ventilation. Utilization of PETCO2 as a noninvasive monitoring substitute for trends in PaCO2 in critically ill patients may be misleading despite establishing an initial PaCO2-PETCO2 relationship.

Adult↗
PubMed1989

Removal of bronchial secretions by two-phase gas-liquid transport.

Net outward wave motion of secretions from airways by two-phase gas-liquid transport is favored by higher airflow during expiration than inspiration. This can be accomplished by IRV in which the controlled mode of mechanical ventilation is adjusted such that the inspiratory cycle is prolonged and the expiratory phase is shortened. Studies were done on six anesthetized, nasally intubated sheep. Simulated mucus was instilled into the bronchi at 15-min intervals during I-E ratio of 1:2.7, 1.9:1, and 3:1. The IRV modes of 1.9:1 and 3:1 promoted transport of simulated mucus outward. Neither systemic blood pressure nor cardiac output were altered by IRV. Thus, IRV might be useful in the management of excessive bronchial secretions in mechanically ventilated patients. However, clinical trials of IRV should take into account its potential for producing adverse hemodynamic effects and barotrauma in patients with compromised cardiac function due to auto-PEEP attendant with its usage.

Animals↗
PubMed1988

Measurement of total lung aerosol deposition as an index of lung abnormality.

Total aerosol deposition in the lung was measured in 100 subjects with various lung conditions. The subjects consisted of 40 normals (N), 15 asymptomatic smokers (S), 10 smokers with small airway disease (SAD), 20 with chronic simple bronchitis (SB), and 15 with chronic obstructive bronchitis (COPD), and a relationship of total aerosol deposition to degree of lung abnormality was investigated. The subjects were categorized by medical history and a battery of pulmonary function tests, including spirometry, body plethysmography, and single and multiple N2 washout measurements. Subjects repeatedly breathed a monodisperse test aerosol (1.0 micron diam) from a collapsible rebreathing bag (0.5 liter volume) at a rate of 30 breaths/min, while inhaled and exhaled aerosol concentrations were continuously monitored by a laser aerosol photometer in situ and recorded on a strip-chart recorder. The number of rebreathing breaths resulting in 90% aerosol loss from the bag (N90) was determined, and percent predicted N90 values were then determined from the results of computer simulation and used as a deposition index. The percent predicted N90 values were 99.7 +/- 14, 86.5 +/- 15, 66.9 +/- 17, 51 +/- 12, and 30.9 +/- 9, respectively, for N, S, SAD, SB, and COPD. All of these values were significantly different from each other (P less than 0.05). There was no difference between male and female but percent predicted N90 values were slightly higher in young than in old normals. Percent predicted N90 values showed a strong linear correlation with spirometric measurements of forced expiratory volume in 1 s and maximum midexpiratory flow rate. However, many of the SAD and SB with normal spirometry showed abnormal N90. These results suggest that total lung aerosol deposition is a sensitive index of lung abnormality and may be of potential use for nonspecific general patient screening.

Adult↗
PubMed1988

Accuracy of respiratory inductive plethysmographic cross-sectional areas.

The present study was undertaken to evaluate whether the respiratory inductive plethysmograph (RIP) 1) reflects changes of cross-sectional area enclosed by its transducer band in the presence of deformations of shape or whether it 2) has a stable base line. Testing of RIP was carried out with a device incorporating a thermally compensated oscillator and digital demodulatory circuitry. This system, introduced to commerce in 1983, superceded the nonthermal compensated oscillatory and analog demodulator circuitry first used in 1977. Testing the effects of changing cross-sectional area was accomplished by stretching a standard RIP transducer band around wooden dowels placed in holes on a peg board grid to form 23 curved and 5 rectangular shapes. The output voltage from RIP was linear for both the curved and rectangular shapes for changes of cross-sectional area within a physiological range. However, the regression line of voltage vs. cross-sectional area for the rectangular shapes was parallel and slightly displaced from the regression line for the curved shapes due to mutual coupling of inductance in the corners. Base-line drift from a RIP transducer band stretched to enclose an elliptical shape was less than 2.5 mV over a 12-h observation period. Current RIP technology accurately reflects changes of cross-sectional area of physiological shapes and has a stable base line.

Humans↗
PubMed1988

Variability of resting respiratory drive and timing in healthy subjects.

Studies of breathing pattern have focused primarily on changes in the mean values of the breathing pattern components, whereas there has been minimal investigation of breath-to-breath variability, which should provide information on the constancy with which respiration is controlled. In this study we examined the variability of breathing pattern both on a breath-to-breath and day-to-day basis by calculating the coefficient of variation (i.e., the standard deviation expressed as a percentage of the mean). By examining breath-to-breath data, we found that the coefficients of variation of tidal volume (VT) and fractional inspiratory time (TI/TT, an index of timing) obtained with an inductive plethysmograph and spirometer were within 1% of each other. Examination of breath-to-breath variability in breathing pattern over a 15-min period in 65 subjects revealed large coefficients of variation, indicating the need to base calculations on a relatively large number of breaths. Less breath-to-breath variability was observed in respiratory frequency [f, 20.8 +/- 11.5% (SD)] and TI/TT (17.9 +/- 6.5%) than in VT (33 +/- 14.9%) and mean inspiratory flow (VT/TI, an index of drive; 31.6 +/- 12.6%; P less than 0.0001). Older subjects (60-81 yr) displayed greater breath-to-breath variability than young subjects (21-50 yr). Use of a mouthpiece did not affect the degree of variability.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Initial experience with a central respiratory monitoring unit as a cost-saving alternative to the intensive care unit for Medicare patients who require long-term ventilator support.

The cost of delivering health care to Medicare patients in intensive care units (ICU), especially those on long-term ventilator support, has become a major financial burden to American hospitals. We established a central station, respiratory, noninvasive monitoring unit (NIMU) on a cardiac telemetry floor where nurse to patient ratio was 1:4 to 1:6 as a cost-effective alternative to the ICU which has a ratio of 1:2. During the first five months of operation, 55 patients were admitted to this unit, of which 11 were long-term ventilator Medicare patients. Seven of these 11 patients were successfully weaned and discharged from the hospital. Overall, a minimum of $21,724 was saved over five months by shifting these long-term ventilator patients from the ICU to the NIMU while quality of medical care remained or exceeded accepted standards. We conclude that alternative health care delivery systems such as the NIMU need to be investigated as safe, cost-reducing substitutes for selected ICU patients to prevent loss of quality medical care in the financial backlash of the present Medicare prospective payment schedule.

Aged↗
PubMed1987

Mucus clearance by two-phase gas-liquid flow mechanism: asymmetric periodic flow model.

Mucus transport by two-phase gas-liquid flow mechanism was investigated with in vitro flow models under asymmetric periodic airflow conditions with nine different liquid solutions with rheological properties similar to human sputum. The flow model was made with 1.0-cm-ID glass tube and positioned either vertically or horizontally. With a constant supply of the test liquids into the model tube (0.5 ml/min), the liquid layer transport speed (LLTS) as well as the mean liquid layer thickness at steady-state condition (hs) was measured in conjunction with various airflow patterns of different expiratory and inspiratory flow rate, breathing frequency (f), and tidal volume (VT). The flow patterns were maintained within the range of normal breathing. In the horizontal tube model, LLTS ranged from 1.14 +/- 0.02 to 3.39 +/- 0.04 cm/min at the peak expiratory flow rate (VEp) of 30-60 l/min. The inspiratory flow rate, as well as f and VT did not affect LLTS. However, LLTS increased with increasing VEp, and at the same VEp LLTS was higher with viscoelastic than with viscous liquid. In the vertical tube model, the upward transport of mucus could not be achieved at VEp lower than 30 l/min particularly with low viscosity and low elasticity fluid. However, at high values of VEp, LLTS was comparable to that in the horizontal tube model with viscoelastic fluid, whereas LLTS of viscous liquid showed 26-40% lower than that in the horizontal tube model. The value of hs was 5-20% of the tube diameter at VEp of 30-60 l/min in both models. These results indicate that effective mucus clearance can be achieved by two-phase gas-liquid flow mechanism in patients with excessive bronchial secretions with biased tidal breathing favoring the expiratory flow and that the clearance can be further promoted by changing rheological properties of mucus.

Elasticity↗