A mathematical model for the ultrasonic measurement of respiratory flow

A mathematical model is developed for the measurement of respiratory air flow, based on the phase shift of ultrasonic pulse trains. A correction is made for the velocity of found as a function of gas composition, moisture, temperature and pressure. Error estimates and calibration procedures as they relate to clinical application are discussed.     

Continuous measurement of flow rate and volume in the nanoliter range

A simple transducer which is based on changes of electrical capacity with volume is described. The system accomodates fluid volumes of several microliters and the resolution is below one nanoliter. The response time of the transducer is about 10 ms. The system is applicable for continuous recording of flow rates in renal collecting tubules. Pulsatile flow in the duct of Bellini is demonstrated.     

Effect of ambient respiratory noise on the measurement of lung sounds

The effect of ambient sounds, generated during breathing, that may reach a sensor at the chest surface by transmission from mouth and nose through air in the room, rather than through the airways, lungs and chest wall, is studied. Five healthy male non-smokers, aged from 11 to 51 years, are seated in a sound-proof acoustic chamber. Ambient respiratory noise levels are modified by directing expiratory flow outside the recording chamber. Low-density · gas (HeO₂=80% helium, 20% oxygen) is used to modify airway resonances. Spectral analysis is applied to ambient noise and to respiratory sounds measured on the chest and neck. Flow-gated average sound spectra are compared statistically. A prominent spectral peak around 960 Hz appears in ambient noise and over the chest and neck during expiration in all subjects. Ambient noise reduction decreases the amplitude of this peak by 20±4 dB in the room and by 6±3.6 dB over the chest. Another prominent spectral peak, around 700 Hz in adults and 880 Hz in children, shows insignificant change, i.e. a maximum reduction of 3 dB, during modifications of ambient respiratory noise. HeO₂ causes an upward shift in tracheal resonances that is also seen in the anterior chest recordings. Ambient respiratory noise explains some, but not all, peaks in the spectra of expiratory lung sounds. Resonance peaks in the spectra of expiratory tracheal sounds are also apparent in the spectra of expiratory lung sounds at the anterior chest.     

Effect of ambient respiratory noise on the measurement of lung sounds

The effect of ambient sounds, generated during breathing, that may reach a sensor at the chest surface by transmission from mouth and nose through air in the room, rather than through the airways, lungs and chest wall, is studied. Five healthy male non-smokers, aged from 11 to 51 years, are seated in a sound-proof acoustic chamber. Ambient respiratory noise levels are modified by directing expiratory flow outside the recording chamber. Low-density gas (HeO2 = 80% helium, 20% oxygen) is used to modify airway resonances. Spectral analysis is applied to ambient noise and to respiratory sounds measured on the chest and neck. Flow-gated average sound spectra are compared statistically. A prominent spectral peak around 960 Hz appears in ambient noise and over the chest and neck during expiration in all subjects. Ambient noise reduction decreases the amplitude of this peak by 20 +/- 4 dB in the room and by 6 +/- 3.6 dB over the chest. Another prominent spectral peak, around 700 Hz in adults and 880 Hz in children, shows insignificant change, i.e. a maximum reduction of 3 dB, during modifications of ambient respiratory noise. HeO2 causes an upward shift in tracheal resonances that is also seen in the anterior chest recordings. Ambient respiratory noise explains some, but not all, peaks in the spectra of expiratory lung sounds. Resonance peaks in the spectra of expiratory tracheal sounds are also apparent in the spectra of expiratory lung sounds at the anterior chest.     

A flow and volume calibrator for respiratory measuring equipment

The design of a simple calibrator for checking the performance of respiratory measuring equipment is described. It is particularly suitable for calibrating the equipment used for obtaining flow/volume curves.     

Continuous measurement of flow rate and volume in the nanoliter range.

A simple transducer which is based on changes of electrical capacity with volume is described. The system accomodates fluid volumes of several microliters and the resolution is below one nanoliter. The response time of the transducer is about 10 ms. The system is applicable for continuous recording of flow rates in renal collecting tubules. Pulsatile flow in the duct of Bellini is demonstrated.     

A flow and volume calibrator for respiratory measuring equipment.

The design of a simple calibrator for checking the performance of respiratory measuring equipment is described. It is particularly suitable for calibrating the equipment used for obtaining flow/volume curves.     

Method of electrophrenic respiration for producing a natural respiratory flow rate using feedback control of tidal volume waveform

A feedback system controlling the tidal volume waveform to avoid producing a high flow rate was designed and assembled on the basis of experimental results in dogs. The static and dynamic characteristics of the tidal volume produced by electrical stimulation were obtained from responses to step inputs of various amplitudes. The static characteristics were approximated by a linear model with a threshold and saturation; the dynamic characteristics were expressed in terms of a time constant and dead time. Both characteristics varied from −20% to +20%, depending on the experimental conditions and/or individual differences. The feedback control system consisted of a proportional + integral + derivative controller, a bias circuit and a controlled system. High gains of the system produced sustained oscillations whose frequencies were in good agreement with predictions derived from analogue computer simulation. The system had a small steady-state error and a fairly rapid transient response.     

Heart rate response to respiratory events with or without leg movements

STUDY OBJECTIVE: This study compares the heart rate responses to the termination of respiratory events, both with and without associated leg movements. METHODS: Heart rate was measured for 15 R-R intervals before (T-15 to T-1) and after (T+1 to T+15) the termination of respiratory events as a change from the baseline rate, defined as the average of 10 R-R intervals occurring before the termination of each respiratory event (T-15 to T-6). Individual heart rate changes of the 21 patients were then averaged separately for 10 respiratory events with and 10 without associated leg movements. SETTING: N/A. PARTICIPANTS: Twenty-one patients with obstructive sleep apnea who had respiratory events both with and without associated leg movements. INTERVENTION: N/A. RESULTS: Maximal heart rate rise for respiratory events with leg movements (7.9 beats per minute) was significantly greater than for respiratory events without leg movements (5.1 beats per minute) (p < .0001). The area under the curve for heart rate increase from T-5 to T+9 was 50.1% higher for respiratory events with leg movements than without leg movements. When respiratory events with and without accompanying leg movements were compared, there were no significant differences in mean duration of respiratory events, mean oxygen desaturation after respiratory events, mean duration of electroencephalogram arousal following respiratory events, or mean heart rate during the baseline period. Heart rate rise did correlate with duration of the leg movements (p < .001) in those respiratory events with leg movements. CONCLUSIONS: Cardiac activation is significantly greater when the termination of respiratory events is associated with leg movements compared to those without leg movements. This exaggerated heart rate response may be an independent consequence of the leg movements themselves, as other features of the respiratory events and associated arousal were not different in the two conditions.     

Effect of radial position on volume measurements using the conductance catheter

A finite-difference computer model has been used to determine the potential distributions arising from a dipole current source aligned parallel to the axis of bounding cylinders. The radial position of this source had large and nonlinear influence on the potentials along the dipole axis. The accuracy of the computer simulation was established from comparison with an analytic solution of a simple geometry. Measurements using a conductance catheter in saline-filled cylinders also demonstrated the dependence of the conductance on the radial position. The dependence of the potential distribution on the radial position of the dipole places limits on the ultimate accuracy of the conductance catheter technique when used for the measurement of ventricular volume. Radial movement of the catheter within the ventricular cavity, resulting in changes in the potential distribution, could explain some artefacts that appear on volume recordings from the conductance catheter.     

Assessment of respiratory flow and efforts using upper-body acceleration

In this paper, an innovative method for estimating the respiratory flow and efforts is proposed and evaluated in various postures and flow rates. Three micro electro-mechanical system accelerometers were mounted on the suprasternal notch, thorax and abdomen of subjects in supine, prone and lateral positions to record the upper airway acceleration and the movements of the chest and abdomen wall. The respiratory flow and efforts were estimated from the recorded acceleration signals by applying machine learning methods. To assess the agreement of the estimated signals with the well-established measurement methods, standard error of measurement (SEM) was calculated and \(\rho = 1-{\rm SEM}\) was estimated for every condition. A significant agreement between the estimated and reference signals was found ( \(\rho = 0.83, 0.82\) and 0.89 for the estimated flow, thorax and abdomen efforts respectively). Additionally, the agreement of the estimated and reference flows was assessed by calculating the ratio of time at the tidal peak inspiration flow to the inspiration time ( \(t_{\rm PTIF}/t_{\rm I}\) ) and the ratio of time at the tidal peak expiration flow to the expiration time ( \(t_{\rm PTEF}/t_{\rm E}\) ). Overall mean and standard deviation of absolute value of differences between \({t}_{{\rm PTIF}}/{t}_{{\rm I}}\) and \({t}_{{\rm PTEF}}/{t}_{{\rm E}}\) ratios calculated for every breathing cycle of reference and estimated flow were 0.0035 (0.06) and 0.051 (0.032), respectively. The presented results demonstrate the feasibility of using the upper-body acceleration as a simple solution for long-term monitoring of respiratory features.     

Circumferential measurement of thoracic wall using a standard respiratory belt

Respiratory gating during imaging to reduce imaging artifacts involves the gathering of image data only at the end of the respiratory cycle. This is commonly performed by a pneumatic respiratory belt to monitor thoracic wall motion during respiration. Such gating has been used for magnetic resonance, computerized tomographic, and nuclear medicine imaging. The goal of this study was to measure the performance of a standard belt used for gating imaging studies. The standard respiratory belt system provided with the Magnetom 42 SP MRI scanner (Siemens AG, Erlangen, Germany) was selected. The belt was connected to a microcontroller-based pressure measurement unit that was connected, to the standard RS-232C serial port of a computer. The signal was compared with that of a strain gauge respiration transducer. The response of the system was tested in vitro both for isometric and isotonic loading. The data measured from the pneumatic belt was linear with different weights of 50 to 1,400 grams with a coefficient of determination (R²) of 0.999. The system was linear for different amounts of stretching (R² of 0.998) within the first 45mm, which is enough for normal breathing. In vivo the pneumatic system seemed more accurate in measuring the constant stretching in apnea than the strain gauge respiratory belt. The results show that it is possible to use a standard pneumatic belt for accurate measurement of thoracic wall movement during imaging and for other purposes as well.     

Forbidden indicators in flow measurement using the saline dilution method

When using the saline conductivity method for measuring flow, the concentration of the indicator (saline), with respect to the resistivity of the flowing fluid (e.g. blood), is an important consideration. Indicators with resistivities that are close to the resistivity of the flowing fluid yield incorrect flow measurements. This ‘forbidden indicator’ is one that has the same resistivity as the flowing fluid, and yields an infinite value for flow. Indicators having greater than ten times, or less than one tenth of, the resistivity of the flowing stream should be used to obtain accuracy.