LETTER TO THE EDITOR
Open Access
Cardiorespiratory fitness: a comparison
between children with renal
transplantation and children with
congenital solitary functioning kidney
Riccardo Lubrano1,4*
, Giancarlo Tancredi1, Raffaele Falsaperla2 and Marco Elli3
Abstract
Children with end-stage renal disease are known to have a cardiorespiratory fitness significantly reduced. This is
considered to be an independent index predictive of mortality mainly due to cardiovascular accidents. The effects
of renal transplantation on cardiorespiratory fitness are incompletely known. We compared the maximal oxygen
uptake (VO2 max) of children with a functioning renal transplant with that of children with congenital solitary
functioning kidney, taking into consideration also the amount of weekly sport activity.
Keywords: VO2 max, Cardiorespiratory fitness, Chronic renal failure, Child, Physical activity, Renal transplant, Solitary
functioning kidney
Dear Editor,
Patients with chronic renal failure (CRF) tend to reduce
their weekly amount of physical activity, with negative ef-
fects on cardiorespiratory fitness and quality of life. After
renal transplant the metabolic deficits induced by CRF are
partially recovered and cardiorespiratory fitness improves.
As we previously reported cardiorespiratory fitness of
transplanted children practicing sports for more than 3 h
per week is similar to normal controls exercising less that
3 h [1]. On the contrary, cardiorespiratory fitness of chil-
dren with a congenital solitary functioning kidney is simi-
lar to normal controls exercising for a comparable
number of hours [2].
We measured the aerobic capacity in relation with
weekly amount of physical activity and glomerular filtra-
tion rate (GFR), comparing a group of children with a
congenital solitary functioning kidney (cSFK) and a group
of children with a functioning renal transplant (Tx).
A standardized pediatric questionnaire was adminis-
tered to all children for investigating the time dedicated
weekly to physical activity [3]. On the basis of the ques-
tionnaire, the children were divided into inadequately
active (<3 h of physical activity per week) and adequately
active (>3 h of physical activity per week).
In the cSFK group we enrolled 30 patients: 15 exercis-
ing more than 3 h/week (cSFK>3) and 15 less than 3 h/
week (cSFK<3). The Tx group was formed with 20 chil-
dren, 10 exercising more than 3 h/week (Tx>3) and 10
less than 3 h/week (Tx<3). In all patients, transplant had
been performed 6 or more years previously, following a
dialysis treatment never exceeding on year. All received
triple immunosuppressive therapy: 12 with tacrolimus
and 8 with cyclosporine.
Maximal oxygen uptake (VO2 max) was measured
during a maximal incremental exercise on a treadmill
(Bruce protocol) consisting of sequential increase in
speed and slope every 3 min until exhaustion (breath-
lessness and leg muscle pain) and/or heart rate ≥85 %
of maximum (calculated with the formula 220 – age
in years). During the exercise the subjects were con-
nected by face mask to a breath-by-breath analyser of
O2 to measure the oxygen consumption (VO2). Max-
imal oxygen uptake (VO2 max) was defined as the
* Correspondence: riccardo.lubrano@uniroma1.it
1Pediatric Department, Pediatric Nephrology Unit, Sapienza University of
Rome, Rome, Italy
4Servizio di Nefrologia Pediatrica, Dipartimento di Pediatria, Sapienza
Università di Roma, Viale Regina Elena 324, 00161 Roma, Italia
Full list of author information is available at the end of the article
© 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Lubrano et al. Italian Journal of Pediatrics  (2016) 42:90 
DOI 10.1186/s13052-016-0299-7
highest level of VO2 reached during the maximal ex-
ercise test expressed as VO2 max/kg (ml/min/kg).
The glomerular filtration rate (ml/min/1.73mq) was
calculated with the creatinine clearance. Informed
consent was obtained from both parents. The protocol
conforms to the guidelines of the Declaration of
Helsinki and was approved by the ethical committee
of the involved institution.
The children in all groups were comparable for age
(years: Tx>3 12.67 ± 3.56; Tx<3 13.90 ± 1.20; cSFK>3
14.18 ± 5.29; cSFK<3 13,5 ± 4.76; p NS). GFR was also
similar in all groups (GFR ml/min/1.73 mq: Tx>3
90.65 ± 22.52;
Tx<3
92.02 ± 21.18;
cSFK>3
99.15 ±
30.63; cSFK<3 101,02 ± 40.12; p NS).
VO2 max in Tx and cSFK was significantly higher in
those practicing sport for more than 3 h per week
(Table 1). Children with a congenital solitary function-
ing kidney had level of VO2 max consistently and
significantly
higher
than
transplanted
patients
(Table 1). There was no significant correlation be-
tween VO2 max and GFR (VO2 max = 26.08 + 0.006;
GFR R^2 = − 0.07).
Our findings show that not only congenital solitary
functioning kidney (cSFK), but also transplanted chil-
dren with regular physical activity exceeding three hours
weekly achieve higher levels of VO2 max. Adequate and
regular physical exercise proves therefore beneficial in
transplanted children improving their ability to cope
with the increased metabolic request of physical stress
and therefore reducing the risk of mortality from cardio-
vascular disease [4].
VO2 max in transplanted children is consistently
lower than single kidney patients with comparable
physical activity. This may be due in part to the
neuromuscular, metabolic, and cardiopulmonary defi-
cits acquired during the exposure to uremic intoxica-
tion before transplant [5], that a functioning graft can
improve but not reverse completely. A combination
of early transplant and prompt resumption of con-
trolled adequate physical exercise post-transplant is
likely to improve further the cardiorespiratory fitness
in these patients, with the known benefits on cardio-
vascular risk and mortality.
Abbreviations
3 h/week: 3 hours a week; CRF: Chronic renal failure; cSFK: Congenital solitary
functioning kidney; GFR: Glomerular filtration rate; Tx: Transplanted children;
VO2 max: Maximal oxygen uptake
Funding
Nothing to declare.
Authors’ contributions
RL participated in the design of the study, performed the statistical analysis
and drafted the manuscript. RF carried out data collection and helped in
performing the statistical analysis. GT carried out data collection and data
analysis. ME participated in the coordination and helped to draft the
manuscript. All authors read and approved the final manuscript.
Competing interest
The authors declare that they have no competing interests.
Consent for publication
Not applicable.
Ethics approval and consent to participate
For each child informed consent was obtained from both parents and the
study protocol conformed to the ethical guidelines of the 1975 Declaration
of Helsinki as revised in 2000. The study was approved by the ethical
committee in our institutions.
Author details
1Pediatric Department, Pediatric Nephrology Unit, Sapienza University of
Rome, Rome, Italy. 2General Pediatrics and Pediatric Acute and Emergency
Unit, Policlinico-Vittorio-Emanuele University Hospital, Catania, Italy.
3DIBIC-Biomedical and Clinic Science Department, “Luigi Sacco”, the
University of Milan-VMS Vialba Medical School, Milan, Italy. 4Servizio di
Nefrologia Pediatrica, Dipartimento di Pediatria, Sapienza Università di Roma,
Viale Regina Elena 324, 00161 Roma, Italia.
Received: 8 September 2016 Accepted: 30 September 2016
References
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Table 1 VO2 max/kg in the four groups of the study
Tx>3
Tx<3
cSFK>3
cSFK<3
VO2 max/kg ml/
min/kg
28.99 ± 1.15 23.22 ± 1.23 46.12 ± 1.09 38.55 ± 1.97
Tx>3 vs Tx<3 p < 0.003; cSFK>3 vs cSFK<3 p < 0.01; Tx>3 vs cSFK>3 p < 0.016;
Tx<3 vs cSFK<3 p < 0.001; Tx<3 vs cSFK>3 p < 0.004; Tx>3 vs cSFK<3 p < 0.001
Lubrano et al. Italian Journal of Pediatrics  (2016) 42:90 
Page 2 of 2

Cardiorespiratory fitness: a comparison between children with renal transplantation and children with congenital solitary functioning kidney.
Lubrano, Riccardo,Tancredi, Giancarlo,Falsaperla, Raffaele,Elli, Marco