The efficiency of the IABP depends on multiple factors, which include: The ability of the ejection system to trace electrical stimulation events and transfer the gas during every cardiac cycle, the patient's hemodynamic status, the anatomical position of the balloon and lastly the volume of the selected balloon.
The variables that affect the size and duration of the IABP inflation with gas and consequently the diastolic increase in pressure, were first published 20 years ago, in an innovative study by Weber et al . They reported that the arterial pressure has direct impact on the balloon performance and that the beneficial effects of the IABP reduces when arterial pressure increases.
The heart rate also affects the balloon functioning. The faster the heart rate, the less the balloon inflation time and the diastolic augmentation.
The relation between the aortic pressure and the volume of the aorta reflects the aortic elasticity and the reduced aortic elasticity means reduced diastolic augmentation.
The closer the IABP to the aortic valve, the higher is the incremented diastolic augmentation .
The effect of the IABP diameter to the patient's hemodynamics was studied by Weber, Janicki, and Walker . They concluded that for any given arterial pressure or aortic size, the greatest augmentation in mean aortic diastolic pressure was achieved with complete occlusion. It is obvious that in 100% occlusion of the aortic lumen, a lesion to the aortic wall and erythrocytes could possibly occur and thus the ideal convergence is thought to be approximetly 90 to 95%.
The balloon volume shall be at least 50% of the stroke volume. In a hypothetical patient with poor cardiac index, the rate of the diastolic incrementation to support an insufficient heart is limited because of the fact that the stroke volume in the given patient is low and thus the ideal balloon volume shall be low. In the course of improvement of the hypothetical s patient s hemodynamics and the more the stroke volume improves, which means that the volume of blood transferred within the aorta at every stroke increases, then the balloon volume of the IABP, necessary to maintain the same level of diastolic augmentation, increments. This fact may suggest that during a period of time from the balloon implantation till the successful removal of the balloon, the performance of corrective interventions to the balloon volume by intervals, based on the patient's clinical status, may be the proper method in order to provide ideal diastolic augmentation, both for the insufficient heart and the heart that shows improvement.
To summarize up to now, the optimum balloon sizing shall be accompanied by adjustments of the balloon size and volume, which shall correspond to the different hemodynamic scenarios.
The equation to calculate the ideal balloon size for every individual patient, shall take into account the patient's hemodynamic state (Arterial pressure, Heart supply, pulses/min) as well as the measurements of the aortic length and diameter from the subclavian artery take off to the celiac axis.
Wiekel et al  after studying the aortographies of 169 patients, concluded that the corrected mid-thoracic diameters varied in size from 16 to 30 mm with 90% of the patients having a diameter over 19 mm. This has been possibly taken into consideration by the manufacturers and thus the balloon diastolic diameter is between 14.7 mm and 18.5 mm.
We reached the same conclusions in our measurements regarding the mid-thoracic diameters.
Paulin et al  suggested that the aorta's size is related to the patient's height, age and weight. After studying a series of aortic diameters, he suggested that the ascending aorta has a relatively fixed lumen, which varies from 22 to 38 mm in adults. The descending aorta has a slightly smaller lumen than the ascending aorta. In addition, the aorta's diameter narrows down after the renal artery take off.
In our measurements regarding the correlation between the difference of the aortic diameter above and below the renal arteries and the patients' height, a weak association resulted. In addition, this difference in the aortic diameter shows no variance between the two genders.
The balloon distal edge shall be "proximal" to the renal arteries' take off, so as to avoid occluding the renal arterial circulation. Swartz et al  studied the arterial dysfunction of the kidneys as a result of the position of the IABP on the take off of the renal arteries. He concluded that such a position of the balloon causes renal ischemia.
In our paper it became apparent that the female population consists of smaller dimensions of skeleton. The mean LSA-CA distance was found to be 22.68+/-1.84. In such a population, even a 34 cc IAB would lie below the take off of the renal arteries, with subsequent «aortic-device mismatch» and negative consequences.
During our study the traditional balloon sizing, based only on the patients height, shows relatively low consistency to the size that would have been selected if the actual length of the internal dimensions of the descending aorta was known. A report by Rastan et al  using CT scans identified IABP malpositions to be a common finding. Anatomic to balloon length mishmatch was found in 68.2% of the cases, with subsequently severe adverse effects.
Yosioka et al  reported that aortic-balloon mismatch could cause abdominal arterial branch obstruction. However, clinical reports of intra-abdominal ischemia due to anatomic-to-device length mismatch are limited [10, 11]. Furthermore, Cho et al  has published in a CT study a 29% rate of renal artery compromise in patient heights of 163 to 183 cm when using a 40-mL balloon size, especially in patients with a small stature. In our study, we confirm by enlarge, these findings: there is only a varying correlation between height and aortic length, which is influenced by age, sex, and possibly ethnic differences .
According to Alexander et al  the rate of the patients over 70 years old that undergo heart interventions, has raised from 7-9% in the 1980's to over 30% in the 2000's. The number of women in need of cardiac interventions has increased from 31% in 1982 to over 40% today. Moreover, a 3-5% of the patients currently live their eighth decade. Sisto et al  mention that an increased number of patients living their eighth decade and who are in need of an IABP support.
Taking into account that that mean age of patients that need a heart operation rises (and the age increases the risk of aortic atherosclerotic disease) and the increasing rate of the women patients population (having smaller aortic diameter) which need an IABP, one would conclude that a more meticulous size selection is required under such clinical conditions, otherwise the aortic environment could be hiding potential risks. Moreover, Wolvek et al  reported that 35.7% of female patients fall into the category of less than 62 in. where the aortic diameter narrows down from 20 mm over the renal arteries to 13 mm below the renal arteries. In such patients, a large IABP size is problematic since 5-6 cm of the IABP fills the "normally narrowed" part of the abdominal aorta (aortic-device mismatch).
The population that we studied was 72.8% male and 27.2% female. The average height of women was 160.97 cm. A 41.2% were less than 162 cm high. Contrary to other studies, our measurements did not reveal a great aortic physiological narrowing of the aorta below the renal arteries.
The aortic measurements in our study are related to the height of the patients and other somatometric measurements (age, sex, external measurement of the thoracic cage). Neither weight nor BSA affect the aortic length or diameter.
In our measurements, the depth of the femoral artery at the inguinal region did not differ between the two genders, though it was proportionate to the body weight.
The possible limitations of the study are related to the relative small number of subjects studied, the fact that most aortas were not atheromatic, so no corkscrew effects or angulations were present and lastly the relative small number of patients over 182 cm high.
Concluding, the guidelines according to which the appropriate size of the intra-aortic balloons are selected, are based on the estmation of the LSA-CA taking into consideration the patients height, age, sex and the easily obtainable distance from the jugular notch to «halfway between the jugular notch and the upper border of the pubic symphysis»; so if LSA-CA is < 21.09 cm use 34 cc IABP, 21.9-26.3 cm use 40 cc, but prepare for «aortic-device» mismatching and if > 26.3 cm use 50 cc.