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Papers by A ar

Respiration Physiology, 1998

Quantitative analysis of the amount of gas entering and leaving the middle ear (ME) was performed... more Quantitative analysis of the amount of gas entering and leaving the middle ear (ME) was performed in patients with central perforation or with ventilating tubes. Patients were divided into a 'balanced pressure group' (BP) where pressure remained close to atmospheric throughout the measuring period and an 'unbalanced pressure group' (UBP) where pressure decreased continuously throughout measurements. The rate of gas gain was 41.0 919.9 vl/h (mean 9SD, n= 17) in the BP group, significantly higher than in the UBP group (21.4 9 9.6 vl/h, n= 8). The rate of gas loss was 34.8 917.7 and 36.1 915.9 vl/h in the BP and UBP groups, respectively. Deglutition frequency was 27 913.4 deglutition/h in the BP group, significantly higher than the deglutition frequency of the UBP group (16 98.9 deglutition/h). It seems that the amount of gas entering the ME per deglutition is rather stable and does not change significantly with ME pressure level. Negative ME pressure may result from decreased gas gain rate due to increased intervals between deglutitions and loss of interdependence between the rate of gas entering and leaving the ME.

Respiration Physiology, 1996

The relative dependence of placental 02 consumption I Mo_,) on 02 supply (SupO2) parameters, and ... more The relative dependence of placental 02 consumption I Mo_,) on 02 supply (SupO2) parameters, and the fraction of aerobic 02 utilization, was studied by in-vitro perfusion of the fetal side of term human placental lobes. Placental M~., was a function of the combined effect of SupO2 parameters (Po:, perfusate flow rate. perfusate effective Oz solubility) and not of each separately. At SupO, greater than 800 1zl/(min • lobe), Mo: saturated at 260 #l/(min • lobe}. No accumulation of O2 debt could be detected even after 2 h anoxia. Adding CN or CO to perfusate did not abolish I~lo,, and a residual M{), of 31-37"~ of control Mo, was measured. In its Mo:, the placenta is a typical conformer tissue. This conformity enables conservation of O2 transfer to the embryo even when placental SupO2 is radically reduced. Only about 60-70~/, of placental M., is utilized in the aerobic respirator 3, pathway, while about 30-4()'~k of the oxygen is used in other pathways.

The Annals of otology, rhinology, and laryngology, 1998

Gas exchange between blood in the middle ear (ME) mucosa and ambient ME gas may be limited by dif... more Gas exchange between blood in the middle ear (ME) mucosa and ambient ME gas may be limited by diffusion through tissue or blood perfusion. In order to study the limiting factors in ME gas exchange, a hole was drilled in the bulla of 14 anesthetized guinea pigs through which a mass spectrometer probe was inserted and sealed in place. The rate at which oxygen (O2), carbon dioxide (CO2), nitrogen, and argon concentrations changed toward their steady state values was recorded. From the exponential fitted curves, gas rate constants (Kg) were calculated. The ratio KCO2/KO2 was 4:1, which is lower than expected from a diffusion-limited process in an aqueous compartment. The different rate ratios of CO2 and O2 indicate a diffusion-limited process. However, the deviation of the KCO2/KO2 ratio from that expected in aqueous solutions may indicate the involvement of a lipid compartment in gas exchange or other physiological mechanisms such as local acidity.

Acta Physiologica Scandinavica, 2003

A mathematical model was developed to identify time periods of atelectasis induction in middle ea... more A mathematical model was developed to identify time periods of atelectasis induction in middle ear (ME) ventilated via ventilating tubes (VT). Atelectatic ears are characterized by a total gas pressure lower than 760 mmHg. Ventilating tubes were deliberately sealed and ME gas content changed in the presence of a preset blood gas pressure. Once sealed, CO2 rapidly diffuses out of the blood via lining tissues into the ME cleft. This results in initially a total ME pressure rise followed by a decrease in subatmospheric pressures. Time periods for atelectasis reformation was determined once ME pressure crossed the 760 mmHg value and continued to decline as the atelectasis reached higher grades. Time periods calculated by the model varied from 18 to 125 min in ME cavities ranging in volume from 0.5 to 3.5 mL, respectively. These results were calculated for conditions of venous blood in the lining mucosa blood and are consistent with prior clinical tests that measured an induced return to previous atelectasis state following the closure of the VT in 33 tested ears within 25-120 min (43 min on average). The model demonstrates that under the above conditions, diffusive gas transfer in relation to blood gas content is the leading mechanism to alterations in ME pressure and volume. It may be used as a tool to determine ME physiological cavity volume of ears with VT.

Respiration Physiology, 1998

Quantitative analysis of the amount of gas entering and leaving the middle ear (ME) was performed... more Quantitative analysis of the amount of gas entering and leaving the middle ear (ME) was performed in patients with central perforation or with ventilating tubes. Patients were divided into a 'balanced pressure group' (BP) where pressure remained close to atmospheric throughout the measuring period and an 'unbalanced pressure group' (UBP) where pressure decreased continuously throughout measurements. The rate of gas gain was 41.0 919.9 vl/h (mean 9SD, n= 17) in the BP group, significantly higher than in the UBP group (21.4 9 9.6 vl/h, n= 8). The rate of gas loss was 34.8 917.7 and 36.1 915.9 vl/h in the BP and UBP groups, respectively. Deglutition frequency was 27 913.4 deglutition/h in the BP group, significantly higher than the deglutition frequency of the UBP group (16 98.9 deglutition/h). It seems that the amount of gas entering the ME per deglutition is rather stable and does not change significantly with ME pressure level. Negative ME pressure may result from decreased gas gain rate due to increased intervals between deglutitions and loss of interdependence between the rate of gas entering and leaving the ME.

Respiration Physiology, 1996

The relative dependence of placental 02 consumption I Mo_,) on 02 supply (SupO2) parameters, and ... more The relative dependence of placental 02 consumption I Mo_,) on 02 supply (SupO2) parameters, and the fraction of aerobic 02 utilization, was studied by in-vitro perfusion of the fetal side of term human placental lobes. Placental M~., was a function of the combined effect of SupO2 parameters (Po:, perfusate flow rate. perfusate effective Oz solubility) and not of each separately. At SupO, greater than 800 1zl/(min • lobe), Mo: saturated at 260 #l/(min • lobe}. No accumulation of O2 debt could be detected even after 2 h anoxia. Adding CN or CO to perfusate did not abolish I~lo,, and a residual M{), of 31-37"~ of control Mo, was measured. In its Mo:, the placenta is a typical conformer tissue. This conformity enables conservation of O2 transfer to the embryo even when placental SupO2 is radically reduced. Only about 60-70~/, of placental M., is utilized in the aerobic respirator 3, pathway, while about 30-4()'~k of the oxygen is used in other pathways.

The Annals of otology, rhinology, and laryngology, 1998

Gas exchange between blood in the middle ear (ME) mucosa and ambient ME gas may be limited by dif... more Gas exchange between blood in the middle ear (ME) mucosa and ambient ME gas may be limited by diffusion through tissue or blood perfusion. In order to study the limiting factors in ME gas exchange, a hole was drilled in the bulla of 14 anesthetized guinea pigs through which a mass spectrometer probe was inserted and sealed in place. The rate at which oxygen (O2), carbon dioxide (CO2), nitrogen, and argon concentrations changed toward their steady state values was recorded. From the exponential fitted curves, gas rate constants (Kg) were calculated. The ratio KCO2/KO2 was 4:1, which is lower than expected from a diffusion-limited process in an aqueous compartment. The different rate ratios of CO2 and O2 indicate a diffusion-limited process. However, the deviation of the KCO2/KO2 ratio from that expected in aqueous solutions may indicate the involvement of a lipid compartment in gas exchange or other physiological mechanisms such as local acidity.

Acta Physiologica Scandinavica, 2003

A mathematical model was developed to identify time periods of atelectasis induction in middle ea... more A mathematical model was developed to identify time periods of atelectasis induction in middle ear (ME) ventilated via ventilating tubes (VT). Atelectatic ears are characterized by a total gas pressure lower than 760 mmHg. Ventilating tubes were deliberately sealed and ME gas content changed in the presence of a preset blood gas pressure. Once sealed, CO2 rapidly diffuses out of the blood via lining tissues into the ME cleft. This results in initially a total ME pressure rise followed by a decrease in subatmospheric pressures. Time periods for atelectasis reformation was determined once ME pressure crossed the 760 mmHg value and continued to decline as the atelectasis reached higher grades. Time periods calculated by the model varied from 18 to 125 min in ME cavities ranging in volume from 0.5 to 3.5 mL, respectively. These results were calculated for conditions of venous blood in the lining mucosa blood and are consistent with prior clinical tests that measured an induced return to previous atelectasis state following the closure of the VT in 33 tested ears within 25-120 min (43 min on average). The model demonstrates that under the above conditions, diffusive gas transfer in relation to blood gas content is the leading mechanism to alterations in ME pressure and volume. It may be used as a tool to determine ME physiological cavity volume of ears with VT.