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PubMed1995

Interference with uterine blood flow by clomiphene citrate in women with unexplained infertility.

OBJECTIVE: To investigate the effect of clomiphene citrate on the uterine blood flow in women with unexplained infertility. METHODS: Twenty-one women who had normal uterine blood flow (pulsatility index [PI] less than 3 from the LH peak to the middle luteal phase of a natural ovulatory cycle) were enrolled in this study. Patients were given clomiphene citrate (100 mg/day) from days 5-9 of the next ovulatory cycle. The PI values measured in the natural and clomiphene citrate-treated cycles were compared using repeated measures analysis of variance. Their correlations with the estradiol (E2) and progesterone concentrations in the treatment cycle were calculated using the Pearson correlation coefficient. RESULT: In the natural cycles of those with normal uterine blood flow, the highest impedance of uterine blood flow was detected at the late follicular phase, then blood flow increased during the luteal phase. In the clomiphene citrate-treated cycles, a statistically significant decrease in uterine blood flow also occurred during the early luteal phase (P < .05). No significant correlation of E2 or progesterone serum concentrations with PI values of the uterine artery could be found in either natural or clomiphene citrate-treated cycles. CONCLUSION: The use of clomiphene citrate decreases the uterine blood flow during the early luteal phase, a periimplantation stage.

Adult↗
PubMed2004

Aneurysmal hypertension and its relationship to sac thrombus: a semi-qualitative analysis by experimental fluid mechanics.

OBJECTIVES: To ascertain the effect of aneurysm thrombus and luminal diameter on arterial blood pressure within the abdominal aortic aneurysm lumen and at the sac wall. METHODS: A life-like abdominal aortic aneurysm was incorporated in a pulsatile flow unit, using systemic blood pressure settings of 140/100 mmHg and 130/90 mmHg (denoted the high and low settings, respectively). Aneurysm sac pressure was measured in the absence of thrombus within the sac. This was repeated after a thrombus analogue (gelatine) was introduced into the aneurysm model in an asymmetric fashion. Luminal and sac wall pressures were compared to the systemic pressure, and to each other, in both blood pressure settings. Statistical analysis was performed using ANOVA in Minitab 13. RESULTS: In the empty sac, the luminal and sac wall pressures were identical to the systemic pressures at the high and low settings. After introduction of thrombus, pressure was transmitted in a monophasic pulsatile fashion, measuring 166/142/151 mmHg (SP/DP/MP) at the sac wall, while the corresponding intraluminal pressure was 164/136/145 mmHg (p<0.001, high setting). By contrast, in the low setting, these readings were 157/133/141 (sac wall) and 160/128/138 mmHg (lumen; p<0.001). The sac wall pressures were significantly higher than the luminal pressures for both high and low settings (p<0.001). CONCLUSIONS: Thrombus has a significant effect on the intraaneurysmal lumen itself and causes localised hypertension with high intraluminal pressures. The differences between the sac wall/luminal pressures may affect regional aneurysm wall biomechanics, but needs further study.

Aortic Aneurysm, Abdominal↗
PubMed2000

[Effects of carotid artery thrombendarterectomy on pulsatile ocular blood flow].

UNLABELLED: Successful operations of clinically significant carotid artery stenosis by carotid endarterectomy (CEA) are leading to a better perfusion in the region of this artery. It still creates problems to make a statement about cerebral and ocular perfusion during the operation. METHODS: In 10 patients who underwent a CEA the pulse amplitude (PA) of the intraocular pressure (IOP) was measured intraoperatively by a pneumotomography (OBF-Systems, U.K.) and the so called pulsatile ocular blood flow (pOBF) was determined. The middle arterial blood pressure (MAP) was taken invasively during the operation. RESULTS: During the clamping phases no PA could be recorded. PA (p = 0.04) and pOBF (p = 0.028) increased on the side which had been operated on. No correlations of PA and pOBF to MAP were found. CONCLUSION: This method can prove an increased pulsatile ocular blood flow after successful CEA.

Aged↗
PubMed2000

Optimal endothelialisation of a new compliant poly(carbonate-urea)urethane vascular graft with effect of physiological shear stress.

OBJECTIVE: to define the optimal seeding conditions of a new stress free poly(carbonate-urea)urethane (CPU) graft with compliance similar to that of human artery with honeycomb structure engineered during the manufacturing process to enhance adhesion and growth of endothelial cells. METHODS: (111)Indium-oxine radiolabeled human umbilical vein endothelial cells (HUVEC) were seeded onto CPU grafts at (a) concentrations from 2-24x10(5)cells/cm(2)and (b) incubated for 0.5, 1, 2, 4 and 6 h. Following incubation, graft segments were subjected to three washing/gamma counting procedures and scanning electron microscopy (SEM). Cell viability was measured using a modified Alamar blue(TM)assay. To test physiological retention a pulsatile flow phantom was used to subject optimally seeded (16x10(5), 4 h) CPU grafts to arterial shear stress for 6 h with real time acquisition of scintigraphic images of seeded grafts using a nuclear medicine gamma camera system. RESULTS: the seeding efficiency of 54+/-13% post three washes was achieved using 16x10(5)cells/cm(2). Similarly in SEM micrographs a seeding density of 16x10(5)cells/cm(2)resulted in a confluent monolayer. Seeded CPU segments incubated for 4 h exhibited significantly higher resistance to wash-off than segments incubated for 30 min (p <0.05). Exposure of seeded grafts to pulsatile shear stress resulted in some cell loss with 67+/-3% of cells adherent following 6 h of perfusion with ongoing metabolic activity. Thus, optimal conditions were 16x10(5)cells/cm(2)at 4 h. CONCLUSIONS: the optimal seeding conditions have been defined for "tissue-engineered" vascular graft which allow complete endothelialisation and high cell-to-substrate strength that resists hydrodynamic stress.

Biocompatible Materials↗
PubMed2002

Relative contribution of wall shear stress and injury in experimental intimal thickening at PTFE end-to-side arterial anastomoses.

BACKGROUND: Intimal hyperplastic thickening (IHT) is a frequent cause of prosthetic bypass graft failure. Induction and progression of IHT is thought to involve a number of mechanisms related to variation in the flow field, injury and the prosthetic nature of the conduit. This study was designed to examine the relative contribution of wall shear stress and injury to the induction of IHT at defined regions of experimental end-to-side prosthetic anastomoses. METHODS AND RESULTS: The distribution of IHT was determined at the distal end-to-side anastomosis of seven canine Iliofemoral PTFE grafts after 12 weeks of implantation. An upscaled transparent model was constructed using the in vivo anastomotic geometry, and wall shear stress was determined at 24 axial locations from laser Doppler anemometry measurements of the near wall velocity under conditions of pulsatile flow similar to that present in vivo. The distribution of IHT at the end-to-side PTFE graft was determined using computer assisted morphometry. IHT involving the native artery ranged from 0.0+/-0.1 mm to 0.05+/-0.03 mm. A greater amount of IHT was found on the graft hood (PTFE) and ranged from 0.09+/-0.06 to 0.24+/-0.06 mm. Nonlinear multivariable logistic analysis was used to model IHT as a function of the reciprocal of wall shear stress, distance from the suture line, and vascular conduit type (i.e. PTFE versus host artery). Vascular conduit type and distance from the suture line independently contributed to IHT. An inverse correlation between wall shear stress and IHT was found only for those regions located on the juxta-anastomotic PTFE graft. CONCLUSIONS: The data are consistent with a model of intimal thickening in which the intimal hyperplastic pannus migrating from the suture line was enhanced by reduced levels of wall shear stress at the PTFE graft/host artery interface. Such hemodynamic modulation of injury induced IHT was absent at the neighboring artery wall.

Anastomosis, Surgical↗
PubMed1996

Hepatic hemodynamics in a patient with nodular regenerative hyperplasia.

Nodular regenerative hyperplasia of the liver is an uncommon condition. Approximately 50% of these patients develop portal hypertension. Few previous reports document the site of increased resistance to blood flow within the liver in this disorder. We measured Doppler waveform patterns of the right hepatic vein by pulsed Doppler ultrasonography and portal, wedged hepatic, and free hepatic venous pressure by intravenous catheter before and after splenectomy in a 47-yr-old woman with nodular regenerative hyperplasia who presented with portal hypertension and pancytopenia. Nodular regenerative hyperplasia was histologically confirmed. Pre- and postoperative measures indicated a marked difference between wedged hepatic venous pressure and free hepatic venous pressure, whereas there was little difference between portal venous pressure and wedged hepatic venous pressure. Doppler waveform patterns of the right hepatic vein showed an unclear pulsatile flow pattern with a decreasing reversed phase. The above data suggest that portal hypertension in nodular regenerative hyperplasia is primarily sinusoidal, similar to that seen with cirrhosis.

Female↗
PubMed2005

The effects of graft geometry on the patency of a systemic-to-pulmonary shunt: a computational fluid dynamics study.

The modified Blalock-Taussig shunt is a palliative operation for some congenital heart diseases. An artificial conduit with antithrombotic surface placed between the subclavian (or innominate) and the pulmonary artery supplies blood to the lungs in defects with decreased pulmonary flow. Clotting of the graft is the main cause of its failure. Stenosis of the arteries is also observed. The objective of the present study was to investigate the flow pattern in the graft to investigate the possibility that clotting is initiated by the stimulation of platelets by high shear stress, and the possible effect of the pathological wall shear stress on the stenosis formation. The model included the left subclavian artery (LSA), the left pulmonary artery (LPA), and the graft. The three-dimensional relative position and size of the arteries was obtained from a CT scan of real anatomy. Four different types of the graft with two different diameters (3 and 4 mm) and two different shapes (straight and curved) of the pipe, and one variable diameter pipe were inserted in the model. A pulsatile flow of 0.81 L/min on average was assumed at the inlet to LSA, and 80% of the flow was directed through the graft. Computer simulations demonstrated a complex flow pattern with eddies and low velocity regions in the arteries at the anastomoses with the graft in all five models. An eddy was also found inside the straight 4 mm graft. A high pathological shear rate was present within the graft, with higher values in the 3 mm grafts. The fractional volume with a high (>2500 L/s) shear rate was between 2.5% and 4.5%, and that with a very high (>7500 L/s) shear rate between 0 and 1.5% of the model volume, and depended on the graft geometry and the phase of the cardiac cycle. Pathologically high (>3.5 Pa) and pathologically low (<1.0 Pa) wall shear stress, which may induce neointimal growth, was found in LSA and LPA. We conclude that the activation of platelets by high shear rate is possible within the graft, followed by their subsequent aggregation in the eddies with a low flow rate. Flow-induced changes of the vessel wall thickness (stenosis) can also appear, especially in the pulmonary artery.

Biomechanical Phenomena↗
PubMed1989

Effects of hydrodynamic forces on coronary production of prostacyclin and purines.

Prostacyclin and purine efflux rates from the isolated rabbit heart in response to variations of flow rate or perfusion pressure were investigated. Increases in coronary flow by 25, 50, and 100% augmented the effluxes of 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) and purines equally, by up to four times. Increases in coronary pressure by 25, 50, and 100% augmented the outflow of 6-keto-PGF1 alpha by up to 20 times, whereas the outflow of purines increased no more than 6.5 times. Neither reduction of perfusate Ca2+ by 50% nor administration of quinacrine (1 microM) affected the basal efflux of 6-keto-PGF1 alpha or its response to an increase in coronary pressure. Both interventions did, however, reduce the pressure-induced purine efflux by approximately 50%. Pulsatile flow did not affect either the outflow of 6-keto-PGF1 alpha or that of purines, in comparison to steady flow at the same rate. The data demonstrate that an increase in coronary pressure activates a specific mechanism for prostacyclin production that appears independent of extracellular Ca2+ and of phospholipase activity.

6-Ketoprostaglandin F1 alpha↗
PubMed1983

Instant shift from continuous flow assistance to paracorporeal diaphragm type pulsatile assistance.

Experiments were conducted implementing a special technique for shifting instantaneously from continuous flow to pulsatile flow assistance by using the assistant heart and obtaining the following results: Within only a few minutes, the shift could easily be made from one type of flow assistance to another on calves with normal hearts. In the 10 calves in which ventricular failure was produced, this instantaneous shift from continuous to pulsatile flow assistance brought about remarkable improvements in their hemodynamics. At the occurrence ventricular fibrillation in 6 of the calves, the return to sinus rhythm was possible with aid of this shift mechanism.

Acute Disease↗
PubMed1996

Early cerebral functional outcome after coronary artery bypass surgery using different acid-base management during hypothermic cardiopulmonary bypass.

BACKGROUND: Cerebral injury can render meaningless an otherwise successful cardiac operation. As carbon dioxide management during hypothermic cardiopulmonary bypass has a major impact on cerebral blood flow during bypass, it may also influence postoperative cerebral function. The objective of this prospective, controlled, double-blind study was to compare the effect of pH-stat (temperature correction of blood gas analyses) or alpha-stat (no temperature correction) on brain function. METHODS: Cerebral function was assessed non-invasively using neurological examination, a neuropsychological test battery, quantitative electroencephalogram and the cognitive evoked potential P300 preoperatively and on postoperative day 7 or 8. Forty-five patients undergoing elective aortocoronary bypass grafting in barbiturate/opiate anesthesia were randomised into a pH-stat-(n = 23) and an alpha-stat-group (n = 22). Membrane oxygenators with arterial line filtration and non-pulsatile flow at a perfussion pressure of 50-60 mmHg were used throughout. RESULTS: One patient in each group developed a new paresis. Among 49 comparisons of cerebral function parameters, only 3 showed significant differences at the 5%-level, i.e. exactly what is expected purely by chance. These differences were too small to be clinically relevant and favored either pH-stat (theta-amplitude) or alpha-stat (subtest 3 of syndrome-short-test, number of mistakes in aiming). CONCLUSION: Under the bypass conditions of this study there was no difference in early cerebral functional outcome between pH-or alpha-stat carbon dioxide management during hypothermic cardiopulmonary bypass.

Acid-Base Equilibrium↗
PubMed2001

Pulsatile ocular blood flow in asymmetric exudative age related macular degeneration.

BACKGROUND/AIMS: Decreased perfusion or increased vascular resistance of the choroidal vessels had been proposed as the vascular pathogenesis for age related macular degeneration (AMD). This study planned to answer the question whether pulsatile ocular blood flow (POBF) was different in patients with asymmetric exudative AMD between eyes with drusen, choroidal neovascularisation (CNV), or disciform scar. METHODS: 37 patients with asymmetric exudative AMD were enrolled in this observational case series study. POBF were measured in both eyes of each subject. Eyes with high myopia, anisometropia, recent laser treatment, and glaucoma were excluded. RESULTS: After adjusting for ocular perfusion pressure, intraocular pressure, and pulse rate, multivariate regression analysis with generalised estimating equation showed POBF was significantly higher in eyes with CNV (1217 (SD 476) microl/min) than the contralateral eyes with drusen (1028 (385) microl/min) (p = 0.024). Eyes with disciform scar had lower POBF than the contralateral eyes with drusen (999 (262) microl/min and 1278 (341) microl/min, respectively, p<0.001). There was no significant correlation between the POBF and the lesion size of the CNV. CONCLUSION: The POBF in eyes with drusen was lower than their fellow eyes with CNV, but higher than their fellow eyes with disciform scar. This finding suggests that haemodynamic differences between fellow eyes in individuals are relevant to the development of CNV and the formation of disciform scar. Further studies on the follow up patients might shed light on the pathogenesis of exudative AMD.

Aged↗
PubMed2001

Pulsatile ocular blood flow in patients with pseudoexfoliation.

PURPOSE: Pseudoexfoliation syndrome is one of the most frequent causes of open-angle glaucoma and is statistically significant associated with a high risk of hypertension, angina, myocardial infarction or stroke and retinal vein thrombosis. The aim of this study was to evaluate the pulsatile ocular blood flow (POBF) in pseudoexfoliation syndrome without (PEX) and with glaucoma (PEG). METHODS: Seventeen eyes with PEX, 17 with PEG and 11 normal eyes of age-matched patients were enrolled. A complete ophthalmological examination included measuring the POBF with the Langham Pneumotonometer as well as the nerve fiber layer thickness by scanning laser polarimetry (GDx). RESULTS: The blood flow parameters, pulse volume and POBF, were statistically significant different between normals and patients with PEG (p < 0.003, t-test). A negative correlation between the intraocular pressure and the POBF was found for all eyes tested. Analysis of GDx? parameters showed a negative correlation for the "number" with the POBF and a positive one for ellipse modulation. CONCLUSION: Although pseudoexfoliation is reported to be a systemic disease measurement of the POBF could not detect any difference between normals and PEX, but was statistically significant different in PEG. Assessments of nerve fiber layer thickness as determined by scanning laser polarimetry also showed a correlation with POBF in some parameters tested.

Aged↗
PubMed1989

[A case of biventricular assist with centrifugal pumps after operation of ventricular septal perforation following acute myocardial infarction].

We applied biventricular assist using centrifugal pumps on a 64-year-old male who has undergone an operation against post-myocardial infarction with ventricular septal perforation. The pump flow was maintained at the level of 2.5 l/m2 in CI, and the pulse pressure 30 to 50 mmHg with IAPB. Complete hemostasis has been achieved prior to use heparin to control the patient's ACT around 200 sec. on the third pumping day. The patient's cardiac function improved in a few days at the beginning, but did not recover enough for weaning from the assist devices. He died on the 8th pumping day, and the autopsy revealed massive old myocardial infarction which is considered to be the major obstacle against the recovery of the cardiac function. There was no edema in any organs. Centrifugal pumps are very useful for ventricular assist in availability and in economy. Its efficacy is comparable with pulsatile ventricular assist devices especially when applied with IABP though there still exists controversy as for the superiority of pulsatile flow in ventricular assist.

Assisted Circulation↗
PubMed2002

Microflow fields in the hinge region of the CarboMedics bileaflet mechanical heart valve design.

OBJECTIVE: The design of bileaflet mechanical heart valves includes some degree of leakage flow on valve closure for the reverse flow to wash the hinge and pivot region of the valve. It is believed that this reverse flow helps to prevent areas of stasis and inhibit microthrombus formation. However, the magnitude of this retrograde flow may also give rise to unacceptable levels of blood element damage and lead to platelet activation or hemolysis as a result of the increased flow velocities through the hinge region. The purpose of this study was to evaluate the hinge flow dynamics of a 23-mm CarboMedics bileaflet mechanical valve (Sulzer CarboMedics Inc, Austin, Tex) and then to compare the results with those of the St Jude Medical 23-mm Regent (St Jude Medical Inc, Minneapolis, Minn) and Medtronic Parallel (Medtronic, Inc, Minneapolis, Minn) valves studied earlier. This comparison allows new insight into the microflow fields within the hinge region of the CarboMedics bileaflet mechanical valve, which have not been previously assessed during its clinical history. METHODS: Two-dimensional laser Doppler velocimetry was used to measure the velocity and turbulent shear stress fields in the hinge regions. To conduct these measurements, exact dimensional models of the bileaflet hinge regions were cast or machined from transparent plastic materials. The experiment was conducted in a pulsatile flow loop with measurements taken at different levels within the pivot and hinge regions. RESULTS: In the 23-mm CarboMedics valve hinge, the phase-averaged forward velocity obtained at the flat level and levels of 190 microm and 390 microm above flat and 1 mm below flat were 0.54 m/s, 0.77 m/s, 0.3 m/s, and 1.0 m/s, respectively. Corresponding values of the peak phase-averaged leakage velocities were 3.17 m/s, 2.91 m/s, 2.52 m/s, and 0.5 m/s, respectively. Corresponding turbulent shear stresses were 5510 dyne/cm(2), 5640 dyne/cm(2), 4380 dyne/cm(2), and 4810 dyne/cm(2), respectively. CONCLUSIONS: The hinge flow dynamics of the CarboMedics bileaflet design lie somewhere in between those of the St Jude Medical and the Medtronic Parallel valve designs. The fluid dynamics of the investigated valve were found to be similar to those of the St Jude Medical valves, although with slightly higher leakage velocities and turbulent shear stresses. This discrepancy may be a result of the sharper corners associated with the hinge design of the CarboMedics valve. It could also be due to the incremental enlargement of the internal orifice area of the St Jude Medical Regent design.

Adult↗
PubMed2006

Pulsatile perfused porcine coronary arteries for microvascular training.

Microsurgery is today an established technique in specialties such as plastic surgery, neurosurgery, and trauma surgery. However, specialized training is a prerequisite for mastering anastomosis of small-diameter vessels or coaptation of nerves in the operating room. The training should be as realistic as possible and thus, laboratory animals such as the rat are preferably used as a substitute. In an attempt to minimize the use of living animals without jeopardizing a realistic training setting, we developed a pulsatile perfused porcine coronary artery model for microsurgical education. The training model consists of a membrane pump that generates a pulsatile flow within a coronary artery of a porcine heart. The pump is commercially available with a dimension of approximately 130 x 100 x 60 mm and a weight of 190 g. The pump is energized by 220 B and the motor is run on a transformed power of approximately 12 V (range, 1.5-12 V). Different fluids from simple saline solution to theoretically whole blood can be used for perfusion. The membrane pump proved to be very reliable during microvascular training because of its convenient size and wide range of feed rate providing a very realistic training setting. A maximum fluid output of 850 mL/min can be achieved. The pump has a high acceptance in microsurgical trainees evaluated by questionnaires during several microsurgical courses. The pulsatile perfused porcine coronary artery system for microsurgical training enables the trainee to work under the most realistic training settings. It proved to be a valuable tool during microsurgical education, reducing the costs and sparing living laboratory animals. Thus, we can recommend this system to anyone who is involved in training and teaching microsurgical skills.

Animals↗
PubMed1993

The effect of topical pilocarpine on pulsatile ocular blood flow.

Ocular blood flow is considered an important factor in determining the extent of visual damage occurring in primary open angle glaucoma (POAG). The effect of topical pilocarpine, a parasympathomimetic vasodilator, on the pulsatile ocular blood flow (POBF) in POAG subjects was studied. A pneumotonometer linked to the Langham Ocular Blood Flow System recorded the intraocular pressure (IOP) pulse from which POBF was calculated. Measurements were taken from 18 POAG subjects treated with both G pilocarpine and G timolol, 2 weeks after withdrawing G pilocarpine and again 1 week after reinstituting full treatment. Recordings from 20 POAG patients treated with only G timolol were taken as control values. There was no significant difference in the IOP or POBF between the controls and POAG patients on dual therapy. Furthermore when G pilocarpine was temporarily withdrawn there was no significant change in POBF despite a significant rise in IOP. The results imply that aqueous pilocarpine has no direct effect on the pulsatile component of ocular blood.

Administration, Topical↗
PubMed1995

Primary stent deployment in occlusive subclavian artery disease.

Primary (without antecedent balloon dilation) Palmaz stent implantation was successfully performed in 27 consecutive patients entering with 31 obstructed subclavian arteries. Stents (n = 50) were successfully deployed, using the brachial (n = 7), femoral (n = 16), or combined (n = 8) approach, to revascularize 31 subclavian vessels [8 occluded (26%); 23 stenotic (74%)], using a 6 or 7.5 French delivery system. The indications for intervention were arm claudication in 8 patients (30%), subclavian steal syndrome in 11 patients (41%), angina pectoris secondary to impaired blood flow to the left internal mammary artery coronary bypass in 6 patients (22%), and recanalization of a left subclavian occlusion to permit central arterial access and performance of a second interventional procedure 2 patients (7%). The percent diameter stenosis improved from 85 +/- 12% to 6 +/- 7% (P < 0.001); and, the peak and mean translesion gradients decreased, respectively, from 56 +/- 35 mm Hg to 3 +/- 4 mm Hg (P < 0.01), and 29 +/- 18 mm Hg to 2 +/- 2 mm Hg (P < 0.01). Procedural complications encountered were one stent dislodgement with migration into and uneventful deployment within the right external iliac artery, and two brachial artery repairs. No acute vessel closures, deaths, myocardial infarctions, cerebrovascular accidents, transient ischemic attacks, or need for transfusions occurred. Therefore, primary subclavian artery stent deployment can be performed using low-profile sheath systems with excellent success (100%), resulting in immediate restoration of pulsatile flow, and few complications. The incidence of lesion recurrence remains for follow-up studies.

Adult↗
PubMedDate not supplied

Deposition and dispersion of aerosols in the airways of the human respiratory tract: the effect of particle size.

Small volumes of aerosols (boluses) were inspired predominantly into the conducting airways of human lungs with a fast operating valve system, injecting preselected aerosol volumes near the end of a clean air inhalation. Particle recovery and bolus dispersion in the exhaled air after various periods of breathholding were investigated by measuring aerosol number concentration directly in front of the mouth with a laser photometer. Inspired and expired flow rates were measured with a pneumotachograph. The effect of particle size on these measurements has been investigated using aerosol particles with aerodynamic diameters (dae) between 0.9 and 5 microns. For aerosol particles smaller than 2 microns, bolus dispersion increases with increasing periods of breathholding (tb). After reaching a maximum, dispersion decreases with even longer tb. An increase in particle size yields a smaller increase in dispersion during the first seconds of breathholding while it is not changed significantly without breathhold. Particle losses during inhalation and exhalation increases with particle size. However, with increasing periods of breathholding, the losses of the smaller particles (less than 1.5 microns) were found to be much higher than expected theoretically, implying particle losses by sedimentation in the same airway structures. The small aerosol particles are deposited in smaller airways than bigger particles. These observations can be explained by cardiogenic mixing during periods of breathholding by pulsatile flow oscillations and confirm measurements with enhanced heart rate as described in an earlier paper. Small particles with restricted settling velocities remained longer in an airborne state in the airways and this leads to a more efficient cardiogenic mixing.

Administration, Inhalation↗