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Biomedical subjects

J Bonassa

Publications and source records attributed to J Bonassa.

6 recordsLinked to original sources
PubMed1995

Mathematical model for a new mode of artificial ventilation: volume assisted pressure supported ventilation: a comparative study.

The patient submitted to artificial ventilation generally is connected to a high impedance flow source with controlled respiratory cycles to assure volume requirements or to a low impedance pressure source with spontaneous cycles to allow synchronization between his effort and system flow delivery. These two types of cycles represent the initial and final stages of artificial ventilation. The patient who needs a volume guarantee and at the same time presents unstable or insufficient inspiratory effort is difficult to manage with assisted cycles which are analogous to the controlled presence of a high impedance flow source. This paper presents a new approach where the respiratory cycles are obtained by the combination of flow and pressure sources using mathematical modeling. These cycles, named volume assisted pressure supported (VAPS) cycles, are compared with conventional assisted cycles showing a decrease in the patient work of breathing (WOB) during assisted ventilation. The theoretical results have been confirmed by clinical trials.

Humans↗
PubMed1992

Volume-assured pressure support ventilation (VAPSV). A new approach for reducing muscle workload during acute respiratory failure.

This study reports the preliminary clinical evaluation of a new mode of ventilation--volume-assured pressure support ventilation (VAPSV)--which incorporates inspiratory pressure support (PSV) with conventional volume-assisted cycles (VAV). This combination optimizes the inspiratory flow during assisted/controlled cycles, reducing the patient's respiratory burden commonly observed during VAV. Different from conventional PSV, VAPSV assures precise control of tidal volume (VT) in unstable patients. Eight patients with acute respiratory failure (ARF) were submitted to assisted ventilation under VAV and VAPSV. Patient's ventilatory workload (evaluated through the pressure-time product, mechanical work per liter of ventilation, and work per minute) and patient's ventilatory drive (occlusion pressure--P0.1) were significantly reduced during VAPSV. This "relief" was more evident among the most distressed patients (p < 0.001), allowing a reduction of more than 60 percent in muscle load, without the need of increasing peak tracheal pressure. Mean inspiratory flow (VT/TI), VT, and effective dynamic compliance were significantly increased during VAPSV, whereas the effective inspiratory impedance decreased. These mechanical advantages of VAPSV allowed a reduction of intrinsic PEEP, whenever it was present. Blood gas values were similar in both periods. We concluded that VAPSV is a promising form of ventilatory support. At the same time that it was able to safely assure a minimum preset VT, VAPSV reduced patient workload and improved synchrony between the patient and the ventilator during ARF.

Acute Disease↗
PubMed1991

[Spherical configuration of the aortic valve].

PURPOSE: To study the normal human aortic valvular ring, and to evaluate the possibility of reproducing its shape artificially. METHODS: The anatomical configuration of six normal aortic valves was studied through the injection of silicone rubber in the ascending aorta. From the resulting casts, epoxi models corresponding to the aortic annulus were obtained. The following parameters were determined: diameter of the base (Db), diameter of the commissures (Dc), height (h) and the Db/Dc and Db/h relationships. The mean value (X) and the standard deviation (SD) of each parameter were studied. RESULTS: The observation of the casts indicate that the aortic valvular ring derives from a sphere. The measures obtained were: Db = 22 +/- 1.67 mm; Dc = mean 19.67 +/- 1.3 mm; h = 16.00 +/- 1.09 mm; Db/Dc = mean = 1.12 +/- 0.04 and Db/h = 1.38 +/- 0.10. Starting from these figures it was possible to define the spheric configuration of the aortic valvular ring, as well as to reproduce it artificially. CONCLUSIONS: The aortic valvular ring has a configuration derived from a sphere or hemisphere. The parameters obtained from the above program, it was possible to reproduce the configuration of the aortic valvular ring and to use it for a bioprosthesis.

Aortic Valve↗
PubMedDate not supplied

[Auto-PEEP effects on respiratory mechanics and blood gases in mechanically ventilated patients]

OBJECTIVE: The purpose of this study was to examine the auto-PEEP incidence and magnitude and the relationship between its reductions and changes in respiratory mechanics and gas exchanges in mechanically ventilated patients addmited in an Intensive Care Unit.METHODS: A prospective study was conducted in seventeen infants undergoing mechanical ventilation due to respiratory or neuromuscular diseases. We have measured blood gases, mean airway pressure, tidal volume, compliance, resistance and time constants of the respiratory system and monitored pressure, flow and volume waveforms and pressure-volume and flow-volume loops.RESULTS: Thirteen patients or 76% developed auto-PEEP and the reduction of its magnitude (from 5.4 -/+ 3.2 to 4.1 -/+ 2.6 cmH2O, p<0.01) showed association to mean airway pressure decrease (from 10.2 -/+ 3.1 to 9.3 -/+ 2.3 cmH2O, p<0.01), tidal volume (from 45.3 -/+ 19.1 to 51.3 -/+ 22.9 ml, p<0.01) and corrected compliance increase (1.02 -/+ 1.20 to 1.13 -/+ 1.41 ml/cmH2O/kg, p=0.05). Expiratory resistance remained unchanged (from 15.0 -/+ 8.6 to 15.7 -/+ 9.4 cmH2O/l/sec/kg, p=0.06). Arterial blood gases showed pH increase (from 7.37 -/+ 0.12 to 7.42 -/+ 0.05, p<0.05) and PCO2 and PO2 decrease (from 40.1 -/+ 11.1 mmHg to 33.1 -/+ 7.4 mmHg, p<0.01 and 65.0 -/+ 13.9 to 58.0 -/+ 12.6 mmHg, p<0.01 respectively).CONCLUSIONS: Auto-PEEP reduction was associated with pulmonary mechanics and blood gases improvement. Knowledge of auto-PEEP presence and magnitude allowed to respiratory system compliance and time constants correction, providing accurate index of the pulmonary mechanics.

Journal Article↗
PubMedDate not supplied

[Airway pressure release in postoperative cardiac surgery in pediatric patients].

OBJECTIVE: Comparison of three modes of MV: intermittent mandatory ventilation with positive end expiratory pressure (IMV + PEEP), APRV and continuous positive airway pressure (CPAP) in children during cardiac surgery post operative with pulmonary hypertension and mild or moderate pulmonary lesion. METHODS: Ten patients were studied with respiratory monitoring (Bear Neonatal Volume Monitor-1) in MV with a continuous flow, time cycled and pressure limited ventilator. The cardiocirculatory variables analyzed were central venous pressure (CVP), oxygen extraction ratio, cardiac rate, systolic arterial pressure, and arterial-mixed venous CO2 difference. Friedman's test (nonparametric) was used to compare the variables in three modalities of ventilation and the Wilcoxon test was used for the variables obtained in two of the modalities. RESULTS: The mean airway pressure (MAP) showed a significant increasing during APRV compared to IMV + PEEP (p = 0.012). The positive inspiratory pressure (PIP), the minute volume and the ratio of oxygen arterial pressure to oxygen inspired fraction (PaO2/FiO2) didn't show statistical difference. During APRV there was a significant decrease in respiratory rate (p = 0.004) and an increase in tidal volume (p = 0.045) when compared to CPAP and IMV + PEEP. In the cardiocirculatory system only CVP showed a significant increased (p = 0.019) during APRV. CONCLUSION: Due to the methodology utilized MAP was higher with APRV resulting in an increased tidal volume without respiratory or cardiocirculatory adverse effects when the three modes were compared. Our results suggest that APRV is a simple and safe method of ventilation.

Child↗